Alone in space, astronaut Charles Van Lyden pilots the Recovery Seven space capsule, guided by the calm voice of Professor Ralph Cornish at Space Control. Van Lyden is now 580 miles (or seven minutes three seconds) from Mars Probe Seven. There is no contact with the probe yet; there hasn’t been for seven months.

‘How do we know they’re still alive?’ asks Van Lyden. ‘They took off from Mars manually,’ Cornish replies. ‘They must have been alive then.’ ‘Something took off from Mars,’ says Van Lyden grimly.

Cornish tells his bearded French colleague, Doctor Bruno Taltalian, that Van Lyden is closing on Mars Probe Seven, but that the astronaut is a bit edgy. ‘Can you blame him?’ Taltalian asks. ‘It is possible he has gone up to rendezvous with a flying coffin.’ Brigadier Lethbridge-Stewart, who stands nearby, asks Cornish if he thinks the astronauts on Mars Probe Seven are dead. Cornish is not hopeful, because in seven months they should have been able to fix a defective radio. Taltalian is concerned that the astronauts’ death could turn public opinion against the space programme. ‘What are you going to tell the public?’ asks the Brigadier. ‘That’s - not my job,’ Cornish replies.

It is the job of reporter John Wakefield, who sits a short distance away, saying to a television camera: ‘In a few minutes we shall know the answer to the question that has been occupying the minds of everyone here at Space Control since Mars Probe Seven took off on its return journey from the red planet nearly eight months ago: what has happened to astronauts Frank Michaels and Joe Lefee? Communications remained perfect on the long outward journey to the red planet and throughout the difficult landing. For a full twelve hours they sent back pictures and reports from the surface of Mars. Both then seemed in perfect health. Then - silence. The world assumed that disaster had overtaken the mission. But when all hope was gone, radio astronomers at Cambridge reported that Mars Probe Seven had blasted off and was heading back to Earth.’

The Doctor, who has been listening to this report in his laboratory, turns the sound down on his television. He moves across to the TARDIS control console, which, removed from the TARDIS itself, stands incongruously in the middle of the lab. He operates various controls. Liz asks him what he is doing. ‘Well I’m trying to reactivate the TARDIS’s time vector generator,’ he tells her. He warns Liz that if this component starts working again, it could send her into the future, particularly if she remains where she is now standing. She is characteristically sceptical, but sure enough disappears with a brief dematerialisation sound - followed closely by the Doctor, as he moves around to the same spot. Liz reappears, disorientated, then disappears again; finally the Doctor and then Liz reappear. The Doctor tells her they were both caught up in the time warp field and projected into the future, but only by about fifteen seconds; from Liz’s point of view, the Doctor explains, he seemed to be the only one who vanished, because she went into the future and he wasn’t there yet. Liz seems bemused by all this. But the time vector generator has packed up again anyway.

The Doctor is surprised to see the Brigadier on television, and wonders what he could be doing at Space Control. ‘Something’s happened to the Mars probe,’ Liz tells him. ‘Mm, the Brigadier thinks it’s his business,’ says the Doctor drily. ‘Ah well, I suppose he’s got to do something to occupy his mind now that he’s blown up the Silurians.’ Liz turns the sound back up on the television, and Wakefield is heard saying: ‘You can see from the radar screen - that’s the screen just to the left of Professor Cornish there - that the recovery capsule and Mars Probe Seven are on convergence. This is a tricky moment for Space Controller Ralph Cornish and his team. The two craft will be linking up in a moment or two, and then we shall know the answer to the mystery that has baffled the world’s scientists for seven months.’

Cornish operates a control, and Van Lyden’s face appears on a large screen in front of him. The astronaut does not have visual contact with the probe yet. He adjusts the attitude of his capsule. Now he sees the probe, and prepares to link up with it. Cornish reassures him that everything looks good. The Brigadier is insistent that Cornish should ask Van Lyden to confirm it really is Mars Probe Seven. Van Lyden gives confirmation - he can see the markings on the probe. But he cannot hear anything from it. Cornish tells Van Lyden to try to make contact one more time before link-up. Cornish speculates that the astronauts’ transmitter might be too weak to reach Earth.

‘Recovery Seven to Mars Probe - do you read me?’ asks Van Lyden tensely. ‘I’m about to initiate link-up. Do you read me?’ There is still no response. Cornish gives the go-ahead for link-up, and Van Lyden expertly executes the manoeuvre, docking his recovery capsule with the larger ship. (In the Doctor’s lab, Liz hands the Doctor a drink as he follows the action intently on television; he absent-mindedly hands the mug back to her.) Van Lyden injects air into the tunnel between the two spacecraft and confirms that the air pressure is okay. As he undoes the clamps on the hatch to the tunnel, he believes he can hear something from the Mars probe: ‘I think they’re opening their hatch. Yes - it’s them!’ Having released the fourth and final clamp, he opens the hatch, and moves through into the tunnel beyond, slightly hampered by weightlessness. His mouth opens in a silent scream, and a piercing unearthly sound fills the air - deafening also those at Space Control. Cornish urgently asks Van Lyden to respond, but there is no answer.

The Doctor has also heard the bizarre sound, on his television. ‘That sound,’ he tells Liz grimly. ‘I’ve heard it somewhere before.’ But to his frustration he cannot remember when: ‘It’s all up here in my mind, the information’s here but I can’t reach it.’ He tells Liz to accompany him to the Space Centre, which is not far away.

At the Centre, Cornish’s assistant Miss Rutherford tells him that a complete check on all their circuits has shown there is no trouble at Space Control end. The Brigadier asks Cornish if he could send up a second recovery capsule to investigate. Cornish tells him this cannot be done immediately, and continues to try to contact Van Lyden, without success. An irritable Taltalian tells Wakefield there is a possibility the sound they heard was ‘some kind of static’, although it is clear he has never heard static like that before. ‘But will you confirm that all radio contact has been lost with the recovery capsule?’ Wakefield asks him. ‘For the time being yes, but temporary loss of communication is not unusual. For instance, when the capsules go behind the moon -’ ‘But those two capsules are not behind the moon.’ ‘You can rest assured that everything possible is being done. Now, if you will excuse me!’ Taltalian storms off, and Wakefield turns to camera: ‘Well as you see there appears to be no apparent explanation for the sudden breakdown in communication, and until the situation becomes clearer the world must wait and hope.’

Driving in ‘Bessie’, the Doctor and Liz gain entry to the restricted area of the Space Centre by nipping under a barrier that was opened for the car in front of them.

While Cornish continues his fruitless attempts to contact Van Lyden in Recovery Seven, Miss Rutherford tells the Brigadier that the two ships have kept their position, and suggests that the problem might be due to an excess of electricity in Mars Probe Seven’s solar batteries. If Lefee and Michaels died on take-off from Mars, there would have been no one to control the build-up of power in the batteries. ‘And that would have affected Recovery on link-up?’ asks the Brigadier. ‘When the capsules were joined, the electric circuits linked automatically,’ Miss Rutherford tells him. ‘Excess electricity in one could have blown all the circuits of the other.’ Van Lyden might have survived, but communication would have been lost.

The Doctor arrives with Liz, blustering his way past security. As his reason for not having a pass, he says he doesn’t believe in them. The Brigadier says he can vouch for the Doctor and Liz. The Doctor wants to know if the sound has been heard again - it hasn’t, but he is convinced it will be. He asks Cornish if he has a recording of the sound, which he believes is a message. ‘I’ve no time to talk to the press,’ Cornish tells him. ‘Quite right, neither have I. But that sound - have you got a recording of it?’ Cornish says that everything at the Space Centre is recorded. The Brigadier introduces the Doctor to Cornish as ‘one of my associates,’ but Cornish just wants him removed. ‘Now you listen to me,’ says the Doctor. ‘That sound was some kind of a message. And it’s going to be repeated.’ ‘Will you please get this man out of here,’ Cornish repeats. ‘We’re trying to save the lives of three astronauts.’ ‘Nonsense, man, you’re doing nothing of the sort. There’s nothing you can possibly do -’

At this moment the unearthly sound comes again, and everyone covers their ears in pain - except the Doctor, who is determined to listen to it. ‘High frequency accelerated impulses,’ he diagnoses. He announces that he will need multiple copies of the recording, unlimited computer time, somewhere to work, and Liz’s help. He tells Cornish he knew the sound would be repeated, because it is a message that has not been replied to: ‘Now we’ve got to break down that code and answer them.’ ‘Answer who?’ Cornish asks. ‘The man’s a fool!’ exclaims the Doctor impatiently. ‘How can I possibly tell who the message is from until I know what it says?’ He starts to patronise Cornish with a simplified explanation, but the Brigadier steps in to try to cool things down, suggesting to the Professor that he might find the Doctor quite useful, and reminding the Doctor that Cornish is the one in charge. The Doctor sees sense and apologises to Cornish for his intrusion, but insists that he be allowed to decode the ‘messages’. Cornish agrees, recognising the necessity of trying everything.

Now the sound apparently comes for a third time, but this time the Doctor identifies a difference - this is not a repetition of the original sound, but a reply to it. He tells the Brigadier he will need worldwide triangulation immediately, to locate the source of this new sound. ‘The message was repeated,’ the Doctor tells Cornish. ‘Perhaps the reply will be. All we can do now is wait.’

Wakefield is keeping his television audience informed: ‘The mystery of Mars Probe Seven has deepened. Seven and a half months of total silence, and now these strange transmissions for which scientists here have no explanation. One theory is that it may be some kind of distress signal. As it is now some hours since the last signal from the capsules, it’s difficult to see what can be done, short of sending up another recovery craft.’

While the Doctor and the Brigadier, standing at a large wall-map of the world, work on locating the source of the reply message, Taltalian gives Cornish his analysis of factors involved in sending up a second recovery capsule. The minimum time until blast-off would be ten days. ‘That’s impossible,’ says Cornish.

The Doctor says that if the reply message came from Earth, they should now be able to identify which country it came from; but they still need to pinpoint the exact location. The Brigadier says that every national radio service is standing by with monitors: ‘wherever that signal’s coming from, we’ll find it,’ he promises confidently.

Taltalian tells Cornish that Recovery Eight was not scheduled for launch until three months from now. Cornish wants the project speeded up, but Taltalian reminds him of the problems with the new fuel injection system. The reply message comes again, cutting through their debate. With the help of Liz, who speaks on the telephone to a contact in France, the Doctor and the Brigadier are now able to establish that the reply message is coming from London. To the Doctor’s frustration, the large screen on the wall can show surface maps of every surveyed planet but cannot show him a map of London (‘Useless gadgets!’) But in any case the map is no longer needed; the Brigadier gets off the phone and announces the results of a local triangulation carried out by UNIT. The exact location of the source of the signal: ‘an abandoned warehouse seven miles from here.’

In the warehouse, a senior army officer (later to be identified as General Carrington) tells one of his men (Grey) to run the message again, this time with all available power.

Three UNIT vehicles filled with armed soldiers, including the Brigadier, arrive at the warehouse. Under the Brigadier’s direction, the UNIT troops pile into the warehouse.

General Carrington tells his subordinate that someone is sure to be monitoring them, but that it may not be so easy for that someone to find them. But at this very moment another of the General’s team, Sergeant Collinson, a big man in civilian clothes, enters with the news that UNIT is outside. ‘That’s very efficient of them,’ says the General. ‘Keep them off as long as you can,’ he orders. ‘Don’t kill anyone unless absolutely necessary.’ But Collinson has a pistol at the ready anyway.

The UNIT troops enter the main area of the warehouse and begin a gun battle with Carrington’s waiting men. Meanwhile Carrington orders the sending of the final transmission - there will be enough time while Collinson keeps the Brigadier’s troops at bay.

Collinson guns down a UNIT soldier. There is a ferocious exchange of gunfire, the two groups of men blasting at each other from the cover of warehouse containers. The opposing sides emerge from cover, and gunplay partly gives way to hand-to-hand fighting. The Brigadier, right in the thick of the action, shoots at targets on all sides. As the fighting rages, the Brigadier points his gun at the escaping Collinson: ‘You can stop right there.’ There is a standoff, the two men aiming their guns at each other. ‘You kill me, my men kill you,’ says the Brigadier, keeping his voice calm and clear. ‘Pointless really.’ A UNIT soldier swings a piece of hanging warehouse equipment at Collinson - and Collinson runs from it, straight into the Brigadier, who drops his gun. Collinson races up a flight of metal steps and draws his own gun on the Brigadier. He smirks triumphantly; there is an agonising pause while the unarmed Brigadier waits to see if he will be shot; but then Collinson, apparently thinking better of it, lets his gun fall to the floor and saunters down the steps with his hands raised in surrender. He is escorted out by UNIT troops, along with other captured members of Carrington’s team.

Carrington orders Grey to trigger the self-destructor on the message-transmitting device. Carrington follows Grey out after firing some shots to lure UNIT into the room. The Brigadier bursts into the vacated room with two UNIT soldiers. The device explodes.

At Space Control, the Doctor complains to Cornish that he needs the use of a computer to decode the messages. Cornish refers him to Taltalian, but the Doctor says Taltalian has been totally non-cooperative. Over a video link, Cornish orders Taltalian to give the Doctor full cooperation.

There are more problems for the space mission: Houston cannot get in contact with the astronauts either, and Athens have reported the build-up of a massive solar flare which will occur some time within the next twenty-four hours. Miss Rutherford points out that the astronauts cannot survive solar flare radiation, and will have to be brought down on remote control. But they are locked on manual control; there is nothing that Cornish or anyone else can do. He sends another message to Recovery Seven, warning about the solar flare build-up and instructing the astronauts to unlock manual control. But from the two linked spacecraft there is still only the same stony silence.

Taltalian demands that the Doctor hand over the reel of computer-tape he is carrying. ‘Do you realise the importance of it?’ the Doctor asks. ‘Rather more than you, Doctor,’ Taltalian replies. ‘So - you understood the message.’ ‘Hand it over!’ Taltalian orders. The Doctor holds out the reel of tape towards Taltalian - and it vanishes into thin air. Taltalian, obviously thrown by this, instructs the Doctor to put his hands up. He demands to know what he has done with the tape. ‘Perhaps he sent it into the future,’ says Liz playfully, remembering the earlier mishap with the TARDIS console. ‘Doctor,’ says Taltalian, ‘are you trying to force me to shoot you?’

The Brigadier now walks into the computer room, and finds himself right in the middle of another dangerous confrontation. The Doctor warns the Brigadier that Taltalian is frightened. Brandishing his gun, Taltalian calls Liz over to him, then grabs her and holds the gun to her head. He backs towards the doorway, then pushes her forwards into the room and makes his escape. The Brigadier goes after him, calling for guards.

The Doctor helps Liz to her feet. He reassures her that Taltalian can safely be left to the Brigadier. She asks the Doctor what he did with the tape, and with a magician’s aplomb he pulls it back out of the air in front of her eyes. He did not send it into the future; it was ‘simply transmigration of object - there’s a great deal of difference between that and pure science, you know.’ Now they need to get to work decoding the tape. Liz identifies the analogue-digital converter among Taltalian’s equipment. Liz takes the reel of tape from the Doctor, obviously capable of operating this machine herself.

The Brigadier returns with the news that Taltalian got away: ‘this place is like a rabbit warren.’ He also tells the Doctor that they found the transmitter at the warehouse, and took several prisoners, one of whom knows a great deal more than he is saying. The Doctor says he would like to speak to this prisoner.

Collinson is languishing in a cell, guarded by a UNIT corporal. The Doctor and the Brigadier are shown in, and the Brigadier asks Collinson if he has decided to talk yet. Collinson does not reply. ‘Why didn’t you shoot me when you had the chance?’ asks the Brigadier. The prisoner remains silent; but when the Doctor urbanely invites him to sit down, he does so. The Doctor realises that Collinson was under orders not to harm the Brigadier, and asks him who gave him those orders. Collinson states that he cannot answer any questions. The Brigadier tells the Doctor that Collinson’s pockets were empty, and that all the labels in his clothes were cut out. ‘You’ve been very thorough, haven’t you?’ says the Doctor to Collinson. The Brigadier warns his prisoner that he is in very serious trouble: ‘I can hold you here on security charges for a very long time.’ ‘Don’t you realise that the men that you were working with were seriously interfering with our space project - and thereby endangering the lives of three astronauts?’ the Doctor asks Collinson. The Brigadier demands answers, but the Doctor advises him that he is wasting his time - the prisoner does know something, but he is not going to tell them what it is. But on his way out of the cell, the Doctor springs a trick on Collinson: he asks him politely if he is being properly looked after, and has had a cup of tea; and when Collinson casually replies ‘yes thanks’, the Doctor roars at him in the manner of a furious army officer: ‘Stand to attention when you’re talking to me and call me sir!’ Collinson instinctively leaps to his feet. ‘Just as I thought,’ says the Doctor. ‘Sergeant, aren’t you?’ Collinson is a soldier - not a deserter, but acting under orders. A message arrives for the Brigadier, and he asks the Doctor to accompany him from the cell.

John Wakefield explains to his television audience: ‘There has been another extraordinary development in the mystery of Mars Probe Seven. The two space capsules, Mars Probe Seven and Recovery Seven, which have been locked together in radio silence, have now separated. But there is still no communication from Charles Van Lyden, nor from astronauts Michaels and Lefee.’

Professor Cornish is still trying to communicate with Recovery Seven, to no avail. A tracking report announces that the two capsules are now approximately seven miles apart. ‘Eleven minutes from scheduled re-entry burn,’ Miss Rutherford reports. The distance between the capsules continues to increase: nine miles…thirteen miles…twenty-five miles… ‘It’s started!’ says Miss Rutherford. ‘Ten minutes too soon!’ Cornish responds. ‘What does he think he’s doing?’

The Doctor assures the Brigadier that there is nothing else they can do for the moment - a re-entry attempt will require at least one orbit of Earth first. In the mean time, the Doctor will check on Liz’s progress with decoding the message, and the Brigadier will run a security trace on the prisoner.

‘Tracking report,’ announces the tannoy voice. ‘Recovery Seven speed now eighteen thousand miles per hour and increasing. Capsule will leave our radar range within three minutes, closing to two point nine five.’ Cornish orders that the capsule be tracked every second from now on.

The UNIT corporal guarding Collinson is attacked outside the cell - a gun is poked into his side and then the mug of hot drink he is carrying is knocked over him. Collinson gratefully makes his escape from the cell; a gloved hand pulls the door shut behind them.

The Doctor can make no sense of the attempted translation of the sound from the capsule: ‘It’s nonsense!’ ‘Perhaps because we’re feeding it nonsense,’ suggests Dobson, Taltalian’s chief assistant. ‘Maybe that sound from the capsule was just freak static.’ Liz suggests that there may be a computer malfunction. Dobson says this is impossible because of the self-checking mechanism, but Liz points out that even that could go wrong, and says she will feed the computer a standard test programme. The Doctor suggests that, instead, she should simply ask it what two and two make. The Doctor asks Dobson how long he has known Taltalian; Dobson says he has been Taltalian’s chief assistant for two years. The machine’s answer comes back as ‘five’. ‘Ah, it’s typical,’ says the Doctor. ‘I never did trust those stupid things.’ But Liz realises that Taltalian must have deliberately sabotaged the computer.

The Recovery Seven is due to reappear in the Northern hemisphere in ten seconds; a tracking report from Massachusetts gives its height as one hundred miles and its speed as twenty thousand (miles an hour) and reducing…eight…seven…six…five…four…three…two…one…zero. The capsule is now in tracking and control range of the Space Centre. Cornish instructs main control to start transmitting. A control room assistant confirms they have contact. Everyone waits tensely, but there is no response from Recovery Seven. A second attempt to transmit to the capsule, with boosted power, also receives no reply. It is now at a height of ninety miles and reducing, with a speed of twenty thousand and holding. ‘It’ll burn up,’ gasps the Brigadier. Miss Rutherford now receives a response from the capsule. Cornish orders a resumption of the transmission, and firing of retro-jets in five seconds. On-screen radar contact is established. Recovery Seven is at a height of eighty-five miles and still reducing, but its speed is down to eighteen thousand and reducing to seventeen thousand…sixteen thousand…

Outside, vast radar dishes monitor the capsule’s descent to Earth.

‘Well,’ announces Wakefield, ‘after what was a pretty rough re-entry by present-day standards, astronauts Van Lyden, Michaels and Lefee will soon be experiencing the buffeting of Earth’s atmosphere when their huge parachutes lower them on the last few miles of their descent. Under normal circumstances, with two or three Earth orbits as a run-up, Controller Cornish could bring them to within one hundred yards of their scheduled landing place. As it is, all we know is that the space capsule is about to land somewhere in the south of England.’

The capsule is dropping at a speed of thirty miles an hour and still slowing down, while drifting south-southwest two degrees with a rate of drift of three knots. The ground-level preparations are completed, and the Brigadier announces that the area will be cordoned off as soon as the capsule lands. Civil aeroplanes have been diverted to avoid its descent. It is now falling at twenty-two miles an hour, reducing to eighteen, at a height of one mile with a drift rate of three knots. Radar contact is now lost, but as the Doctor explains to the Brigadier, that is normal in the last few seconds before landing. ‘We’ve made it,’ says Miss Rutherford. The Doctor and the Brigadier congratulate Cornish, but his concern now is whether or not the astronauts are alive.

A short while later, the Doctor, the Brigadier and Cornish arrive at the Recovery Seven capsule’s landing place in the countryside, where UNIT troops are already waiting. Cornish uses a radio transmitter to tell the astronauts inside the sealed capsule that they are safe and have landed; but there is still no answer from inside, and the hatch does not open. Meanwhile General Carrington and one of his men observe from the cover of trees. Cornish speculates that the astronauts may be unconscious. The Brigadier suggests that they try to open the capsule themselves. But this seems impossible: the mechanism has been jammed, or (as the Doctor suggests) the astronauts have locked it from the inside. The Brigadier now suggests they cut the capsule open, but Cornish says that that would be too dangerous for the astronauts. The Doctor’s proposal is to take the capsule back to the Space Centre. With Carrington’s man listening in on headphones, the Brigadier orders over his radar transmitter that UNIT Control clear a route between the capsule and the Space Centre. ‘Excellent,’ says Carrington. ‘Couldn’t be better.’

Cornish heads off back to the Space Centre, while the Brigadier stays with the convoy that will transport the capsule there. The capsule is hoisted by crane onto the back of a large transporter vehicle. ‘See you at the Space Centre,’ the Brigadier calls to the Doctor, who is fiddling with Bessie’s engine. ‘If you make it.’ The Doctor looks up furiously at this aspersion on his car’s reliability. The Brigadier gets into the transporter vehicle. The Doctor gets Bessie started, but she sounds distinctly unwell. The convoy moves off with the capsule. Bessie’s engine cuts out before she even completes the turn necessary to follow the convoy. The convoy moves slowly over a bridge, flanked by motorcycle outriders. After a delay, the Doctor gets Bessie started and follows.

A helicopter moves in low over the convoy. The pilot wears dark glasses and a kind of gas mask. Smoke bombs rain down from the helicopter, throwing the transporter driver and the motorcycle outriders into confusion. The helicopter sets down, and some of Carrington’s men emerge from it brandishing hairdryer-like weapons that function as stun guns. The helicopter lifts off again as a battle ensues. The Brigadier is felled by a blast from a stun gun. This time UNIT comes off worse, as Carrington’s men make short work of the motorcyclists with their stun guns. The transporter vehicle is captured. One UNIT soldier clings to the door of the departing helicopter, but is pushed off it and falls to the ground. Both the helicopter and the captured vehicle bearing the capsule are able to leave the scene without further resistance from UNIT.

Bessie is now making better progress. In the cabin of the transporter vehicle, Collinson removes his gas mask. General Carrington sits beside him. Confronted by the oncoming transporter, the Doctor thinks quickly and brings Bessie to a stop in the middle of the road, blocking its path. The transporter comes to a halt, and the Doctor explains, in a rather fragile elderly-sounding voice, that if the men want his car shifted they will have to help him move it. Carrington and Collinson get out, and obligingly push Bessie to the side of the road. But before they take their hands off the rear of the car, the Doctor quickly flips a switch labelled ‘anti thief device’. The two men find their hands stuck to the back of the car as if glued to it. ‘Thank you very much,’ says the Doctor. ‘Don’t worry, it’ll switch itself off - eventually.’ The men are helpless to intervene as the Doctor gets into the transporter vehicle and drives off with the capsule.

At the Space Centre, the Brigadier is explaining to Cornish about the hijacking of the capsule, and the disappearance of the Doctor. He is astonished when he sees both the capsule and the Doctor safely installed at the Centre. ‘I brought it here,’ says the Doctor proudly. The Brigadier has found Bessie, but with no villains attached. ‘Can’t have got that force-field strong enough yet,’ the Doctor muses. Liz telephones the Doctor to say that she thinks she is making progress with the decoding, and he leaves to join her. Equipment is being connected that may enable Cornish to make contact with the astronauts inside the capsule.

The Doctor is with Liz and Dobson, checking Liz’s work: ‘You’re right Liz, this is a definite attempt at pictographic communication.’ The repetition of certain symbols shows that it is not just a series of random patterns. The Doctor suspects that the symbols come from ‘an alien intelligence so different this is the only way they can communicate.’ Before Liz can draw him into further explanation, the Doctor announces that it is ‘high time the Brigadier and I had a talk to the top man.’ Liz leaves with the Doctor. Left behind, Dobson makes a mysterious telephone call: ‘They’ve started to crack the code.’

The ‘top man’, government minister Sir James Quinlan, is giving the Doctor and the Brigadier a hearing in his office, but appears hostile and unhelpful. The Brigadier explains about Taltalian’s treacherous behaviour, which was in spite of the fact that Taltalian was checked and double-checked like everyone else on the project. Quinlan claims to be amazed because he has known Taltalian for years. ‘The question is, who else is involved?’ says the Doctor impatiently. Quinlan reminds them that at least they have the capsule back; but the Doctor points out that the astronauts still refuse to come out. Quinlan promises the Brigadier that he will ‘initiate a top-level investigation immediately,’ and the Doctor recognises that they have been fobbed off. The Brigadier gets the Doctor out of Quinlan’s office before the Doctor becomes too rude. After their departure, Quinlan summons Taltalian out of hiding. ‘Won’t you sit down?’ Quinlan asks.

As the Doctor and the Brigadier arrive back at the Space Centre, Liz and Cornish are trying unsuccessfully to make contact with the astronauts inside the capsule. For a second time, the Brigadier suggests that they cut the capsule open; Cornish says he has men standing by with thermal lances. Suddenly Liz starts to receive a signal from inside the capsule.

Taltalian is worried that UNIT have the capsule; Quinlan knows they have started to crack the code as well. But Quinlan assures Taltalian that the UNIT problem has already been dealt with: ‘They’ve got quite a surprise coming.’

The capsule is cut open with thermal lances. A section is lifted away, and Cornish climbs up a ladder to look inside. ‘It’s empty!’ he exclaims. The Doctor climbs up a second ladder and sees that this is true. The Doctor grimly asks Liz to try communicating with the astronauts again. She does so, and the deadpan voice of Van Lyden is heard again - coming from a tape recorder inside the capsule. The recording was triggered by the speech of the people outside. ‘Then where are the astronauts?’ asks the Brigadier. ‘Someone wanted us to believe they were still inside there,’ says the Doctor. He checks with Cornish that the tape recorder is not a standard part of the astronauts’ equipment - someone put it there to delay the opening of the capsule. ‘Now suppose the astronauts were still in there when it landed,’ suggests the Doctor, ‘and later they were removed.’ The Brigadier dismisses this as impossible, because the capsule has been guarded all the time, but it soon comes to light that this is not true: Cornish and Liz explain that earlier they were sent back to the control room while UNIT men performed a security check of the area. But the security check was a phoney, the Brigadier having given no such order. ‘Well there you are then,’ says the Doctor. ‘The bogus patrol turns up, clears the area, and removes the astronauts at their leisure.’ ‘Who would want to kidnap three astronauts?’ asks Cornish. The Doctor suggests it might well be the same people who replied to the message. The Brigadier sets off to have a word with his guard commander. The Doctor is on the point of leaving with him when Liz calls him back: ‘The Geiger counter - it’s on maximum,’ she says. ‘The interior’s radioactive. If anyone was in there, they’re as good as dead.’

Three space-suited figures lie side by side behind a transparent screen in a laboratory. Having had a look at them through the screen, Carrington is informed by a white-coated scientist, Professor Heldorf, that the space-suited bodies contain ‘two million rads - scientifically they should be dead.’ But they are not. Heldorf tells Carrington that they resisted violently when an attempt was made to remove their helmets, and Carrington angrily reminds Heldorf that he was ordered not to remove their protective clothing. ‘General Carrington,’ Heldorf protests, ‘these men have received massive doses of radiation. They need total blood transfusions immediately. They need antibiotics, cortisone injections. You don’t understand the situation. We must reduce the radiation.’ Carrington tells him to increase it. ‘Are you mad, that would be murder.’ Carrington tells Heldorf that ‘the radiation which affects these men is something totally new to us. To survive it, they have become dependent on it.’ As a scientist Heldorf finds this hard to believe, but Carrington gives his order: ‘You must feed them radiation. Otherwise they will die.’ ‘No no no, you can’t ask me to do that.’ ‘I’m not asking you,’ Carrington says.

‘I don’t think you can sweep all this under the ministry carpet, Sir James,’ the Doctor is saying to Quinlan, confronting him in his office along with the Brigadier and a flamboyantly dressed Liz. ‘Someone in authority has done this.’ Quinlan points out that the astronauts were in the Brigadier’s charge; but the Brigadier replies that they were taken from the Space Centre by two army officers with genuine authorisation papers, passes made out in the names of two non-existent officers, plus a platoon and an army vehicle of the latest design: ‘Not the sort of thing you buy from an army surplus store.’ Quinlan compliments the Brigadier on his thoroughness, but remarks it is a pity that he has no explanation to offer. The Doctor tells Quinlan they have not come to offer explanations, but to demand them - from him. Quinlan says that he will introduce the Doctor, Liz and the Brigadier to the man who can explain the truth of the situation. He calls into his office none other than - ‘General Carrington, head of the newly formed Space Security Department,’ Quinlan announces. Liz recalls that Carrington was an astronaut on Mars Probe Six. Carrington confirms this, then invites the Brigadier (who has stood to attention in the presence of a superior officer) to sit back down.

Carrington offers his apologies: ‘I can only ask you to believe that everything I have done has been for the good of us all.’ The Doctor wants to know whether this includes sending coded messages to Mars Probe Seven and kidnapping three astronauts; and Liz would like an explanation for being held at gunpoint by Taltalian. Carrington explains that Taltalian was under strict orders to make sure they did not have access to the computer. ‘You see,’ he explains, ‘every astronaut is issued with an emergency code, only to be used in the ultimate emergency - the code you’ve been trying to crack. The message we received from Mars Probe Seven told us that the deep-space capsule had passed through a hitherto unsuspected high-density radiation belt on its way back to Earth orbit.’ Carrington explains that for security reasons Space Control were not informed. ‘Then why wasn’t I informed - sir?’ asks the Brigadier. Carrington replies: ‘UNIT is an international organisation, and the Government wanted to keep this in its own hands.’ ‘But why all this extraordinary behaviour?’ asks the ever-sceptical Doctor. ‘Well, surely radiation is a normal hazard of space travel.’ ‘We believe this radiation to be a different kind,’ says Carrington. ‘We believe it to be self-sustaining and highly contagious, and that it could spread like a plague, contaminating the entire planet.’ Quinlan states that they do not want the public to become panic-stricken. At first the Doctor seems to accept, along with the Brigadier and Liz, that all that has occurred is a breakdown of communication; but then he reveals he is still not satisfied: ‘I should like to take a look at these mysteriously radiated astronauts for myself, if I may.’ Carrington dismisses this as unnecessary, but when the Doctor insists, Quinlan agrees. Carrington says he will take the Doctor to see them now - ‘but I can assure you they’re perfectly safe.’

The three space-suited figures are being marched at gunpoint out of the laboratory by a group of three thugs. Heldorf’s protests are ignored. On his way out, the thugs’ leader, Reegan, tells the other two men to go back by the direct route - ‘when you’ve finished here.’ After Reegan’s departure, Heldorf tries to put up a fight, but is brutally shot down. After the briefest of scuffles, so is his fellow scientist.

Outside, the three space-suited figures climb into the back of a tradesman’s van. Reegan tells his two companions to ride in the back with them: ‘They won’t hurt you. You’ve got guns, haven’t you?’ The two men reluctantly climb in, and Reegan gets into the driver’s seat. The van drives away.

Seconds later, the Doctor arrives in Bessie with Carrington, the Brigadier and Liz. Carrington opens up the outer door of the lab, and all go in. Inside, Heldorf and his colleague lie dead. The Doctor kneels at Heldorf’s side and gently closes the dead man’s eyes. The Brigadier asks Carrington where the telephone is, and Carrington directs him to it. While the Brigadier makes his phone call to announce a yellow alert, the Doctor challenges Carrington: ‘Perfectly safe, were they?’ Carrington claims he cannot understand what has happened. Liz has found the radiation records for the ‘missing astronauts’: over two million rads. ‘They couldn’t possibly have survived that amount,’ she says.

Reegan’s van stops at a vast gravel pit, with cranes, lakes, and mountains of gravel. Having donned a radiation suit, he drags his two dead colleagues out of the back of the van, and dumps their bodies and their guns unceremoniously on a gravel slope. He tucks something inside the right jacket pocket of each dead man, then makes his way with difficulty backwards up the gravel hill, pushing gravel down with his feet to cover the bodies. Overhead, heavy gravel-shifting machinery swings through the air; it will not be long before Reegan’s work is finished for him and the two bodies are buried completely. He drives away in the van. After a short while he stops again on the road, and at the touch of a control he changes the van’s registration plates (from ‘KBF979H’ to ‘YLD259H’) and its advertising side-panels (from ‘Hayhoe Launderers Ltd.’ to ‘Silcock Bakeries’). Then he moves off again.

UNIT troops have arrived at Heldorf’s lab and are working alongside the Doctor and Liz. Liz confirms the exact radiation figures as 2,102,462 (rads). Carrington appears anxious that the Doctor should realise the importance of retrieving the missing astronauts; the Doctor says he does, and for that reason must be allowed to continue his work undisturbed. The General apologises. ‘You know, it’s the most extraordinary thing,’ the Doctor says to Liz, looking at the readings. ‘Those astronauts were emitting radiation like walking reactors.’ ‘But radiation destroys human tissue,’ says Liz. ‘Yes,’ says the Doctor enigmatically, ‘I know.’ The Brigadier comes in and tells Carrington that the radioactive trace goes to just outside the building and then it vanishes. Carrington concludes that the astronauts were taken away in a vehicle. The Brigadier asks the General why anyone should kidnap them. ‘Contagious radiation,’ Carrington replies. ‘Could be a terrible weapon in the hands of a foreign power.’ The General tells the Brigadier that only his immediate staff knew the location of the laboratory. ‘And Sir James Quinlan,’ adds the Brigadier meaningfully. ‘And his immediate staff.’ ‘Well I can tell you where your three astronauts are,’ the Doctor announces. ‘They’re still in orbit.’ ‘But they came down in the capsule,’ Carrington protests. ‘They were here, I saw them.’ ‘No, you saw three space suits,’ says the Doctor. ‘I don’t know what came down in Recovery Seven - but it certainly wasn’t human.’

The three space-suited figures once again lie side by side behind a transparent screen, this time in the laboratory of a timid, diminutive white-coated scientist, Lennox. ‘They must be dying,’ he says anxiously to Reegan. ‘I don’t think so,’ Reegan replies coolly. Lennox says the astronauts should be in a hospital intensive care unit, but Reegan tells him: ‘You’ve got your instructions, Lennox.’ Lennox insists on being addressed as ‘Doctor Lennox’. ‘I thought they took that away from you,’ Reegan takes pleasure in reminding him. Reegan reports over the telephone that all is well: ‘Lennox is looking after them. No, no trouble at all. I just dropped those two off on the way.’

At the Space Centre, the Doctor has explained to Cornish that he believes the three astronauts are still in orbit in Mars Probe Seven. The astronauts’ life support systems will be running down, and another recovery capsule must be sent up as quickly as possible. Cornish has to telephone Quinlan for permission, and the Doctor is unhappy about this. Sure enough, Quinlan does not agree to the launch of another recovery capsule, on the grounds that it is not certain that the astronauts are still in space, and ‘the Government simply will not authorise the expenditure on so little evidence.’ ‘We’re not talking about money, we’re talking about human life,’ Cornish protests. ‘Sir James, I am going to start preparations now. Unless I get your full backing, I’ll call a press conference and tell them the entire story.’ ‘I would advise you not to do that,’ says Quinlan. ‘Then you’ll have to make sure that I don’t have to,’ replies Cornish, and hangs up - leaving Quinlan to stew, along with Carrington, who is with Quinlan listening in to the call. Quinlan is unsure what to do to stop the second recovery capsule.

In Lennox’s laboratory, one of the captive figures comes to the transparent screen, and presses the palms of its hands against it. Lennox wants to go in to examine ‘those men’, but Reegan reminds him that that would be against orders. Lennox is puzzled because the radiation count has dropped drastically, yet far from showing signs of recovery, one of their captives has collapsed. Reegan points out that he was hired simply to get them here. ‘You weren’t hired to let them die,’ Lennox says. ‘Do you think you’ll get your money if they’re dead?’ This hits home, and Reegan decides to go in and have a look at the space-suited figures. He puts on protective gloves, but no other protective clothing, as the radiation has dropped and he does not intend to spend long with them. He goes in and helps the collapsed figure get up. But it knocks him effortlessly aside, and emerges into the main part of the lab to confront Lennox. Ignoring Lennox’s protests that he just wants to help the astronauts, the figure advances remorselessly upon him without uttering a word. Terrified, Lennox scurries up the laboratory steps to escape, but finds the door at the top locked. The figure closes on him, and he screams as it raises its right hand menacingly to his face. But at the last moment the figure seems to lose all its strength, and collapses. Reegan rejoins Lennox, and the terrified Lennox rebukes him for locking the door. Reegan tells Lennox to shut up and to help him get the collapsed captive back in with the others. The telephone rings; Reegan answers and agrees to ‘take care of them’. ‘Listen, about those astronauts,’ he adds. ‘Isotopes? Well you’d better get them over here.’ Reegan tells Lennox: ‘I’ve found out what’s wrong with these fellas. They don’t need less radiation - they need more!’

At the gravel pit, a workman makes an unpleasant discovery.

In the sealed-off part of the lab, Lennox, wearing protective clothing, provides the ‘astronauts’ with radioactive isotope. He emerges morosely.

At the Space Centre, Cornish gets off the telephone and reports irritably to the Brigadier and the Doctor that ‘everything’s taking just that little bit longer than it should.’ He suspects that Quinlan may have something to do with the delays, but says that he could not prove it.

Lennox tells Reegan he feels as if he has just murdered the ‘astronauts’. Reegan tells him just to keep doing as he is told. The telephone rings again; Reegan answers and says he will open the front door. Lennox sees that the space-suited figures are starting to revive. ‘I told you they’d be all right,’ says Reegan. ‘They thrive on the stuff.’

The Brigadier receives a telephone message saying that two bodies have been found in a gravel pit in Hertfordshire; they died from radiation.

‘You’re a kind of a scientist,’ Reegan says grudgingly to Lennox. ‘Do you know these two?’ He shows him photographs of the Doctor and Liz. ‘Yes, I - I think I met the girl once. She was doing research at Cambridge. Why?’ ‘Seems like they’re getting in the way,’ Reegan answers. ‘I’ll need to deal with them.’

The Doctor takes another reading inside the Recovery Seven capsule and announces that, to his surprise, the radioactive contamination has almost vanished. ‘If you can’t get Recovery Eight ready in time, you can use this capsule,’ he suggests. ‘Providing we can get the three thousand tons of rockets to go underneath it,’ says Cornish. A UNIT soldier brings Liz a written message, apparently from the Brigadier: ‘He wants us to go down to Hertfordshire to look at those bodies,’ says Liz. The Doctor says that rather than go with Liz, he will stay at the Space Centre and get the capsule fully operational.

Liz drives out of the Space Centre complex in Bessie. As she drives along, another car emerges from a side road and starts to follow her.

The Brigadier disturbs the Doctor’s work on the capsule. ‘You’re back soon,’ the Doctor observes. The Brigadier says that he started back an hour ago. The Doctor tells the Brigadier about the message they just received; the Brigadier did not send it. ‘I’ll get after her,’ the Brigadier says, and hurries away.

The man whom Liz pushed off the walkway manages to get back on to it, and, surprisingly, helps his companion pull Liz to safety. She is frog-marched away between the two men.

A short time later, Reegan forces Liz roughly down the stairs into Lennox’s laboratory. ‘I’ve brought you some company,’ he tells Lennox. Reegan explains that he could not get the Doctor because he did not keep the appointment, but that Liz is a scientist and can give Lennox a hand. Liz recognises Lennox, and seems horrified to see him here. Lennox informs Reegan that the space-suited captives are surviving, but only just. Reegan tells Liz to start making herself useful. ‘What if I don’t?’ she responds gamely. ‘I might just lock you in there with them,’ Reegan replies, with a movement of his head towards the radiation-soaked ‘astronauts’.

The Brigadier tells Carrington that he has issued Liz’s description to every police force in the country. Carrington is scathing about this measure, but the Brigadier assures him that it was just a formality. Carrington has been examining the items planted by Reegan on the two bodies at the gravel pit - a newspaper cutting in a foreign language, and a comb with the maker’s imprint on it in the same language - which nicely support the General’s story of the astronauts having been kidnapped by a foreign power. The Doctor carefully examines the comb, using (in his right eye) one of the eye-pieces normally used for scrutinising precious stones. ‘Very remiss of them, keeping this,’ he remarks sceptically. The Brigadier suggests that it could have been planted. ‘No,’ says Carrington, ‘the only people who could set up an organisation of this size would be foreign agents with enormous resources behind them.’ The Doctor looks unconvinced. ‘And hair combs,’ he adds. ‘They want to use the radiated astronauts as a weapon,’ says the General. The Doctor reminds him that the astronauts are actually still in orbit. Carrington dismisses this as ridiculous. The Doctor tells him: ‘When your Professor Heldorf had the aliens in his care, he started to record some sort of radio communication impulses.’ ‘Astronauts do have walkie-talkies in their helmets, you know,’ replies Carrington. ‘Then why didn’t Heldorf talk to them?’ ‘Yes, well perhaps he was recording the level of radioactivity in their bodies,’ Carrington suggests uncertainly. But the Doctor does not think so. He wants to go to the Space Centre to use their computer: ‘I trust your man Taltalian won’t hold a gun on me this time.’ Carrington tells the Doctor that there is nothing to be gained by deciphering the impulses; their objective should be to find the missing astronauts. The Doctor has to tell Carrington for a third time that the astronauts are still in orbit: ‘My objective is to find out what these aliens are trying to say to us.’ Carrington looks very unhappy about this.

At the Space Centre, Taltalian is working with Cornish, planning the launch of a new recovery mission. 1,297 tons of conventional ‘K’ fuel are available, and a further 2,000 tons of liquid fuel are in production; but the liquid fuel is the highly volatile new M3 variant, which was not intended for manned space-flight. Cornish says that they have will have to use it. If the liquid fuel is used alone, the astronaut will be crushed at lift-off, so he suggests reducing the G-force by mixing M3 with the conventional fuel. Taltalian says he will compute this idea, but adds that Cornish will still have to get his rocket built. Cornish says that Quinlan is putting up every possible objection. ‘What do you expect?’ asks Taltalian. ‘This Doctor’s theory is ridiculous.’ Cornish challenges Taltalian: ‘Do you intend to commit more sabotage?’ Taltalian irritably reminds Cornish that earlier he was simply following Carrington’s orders: ‘And I have computed the assembly of the rescue rocket as you asked me.’

The Doctor walks in quietly behind Taltalian. He pulls a pencil from his left breast pocket and pokes it into Taltalian’s back. ‘You’re not armed, I hope,’ he says mischievously. Taltalian assures him that he would not have used the gun on a fellow scientist. The Doctor says he is much relieved, and requests the use of the computer. Cornish agrees: ‘And I’m sure Doctor Taltalian will be only too pleased to help you,’ he adds ironically. ‘When you have a moment I’d like to see you in the control room about the recovery capsule,’ Cornish says to the Doctor, and leaves. The Doctor tells Taltalian he wants to programme the radio communication impulses into the computer; he suspects some sort of pattern in the impulses. Taltalian warns the Doctor that this could take a long time, but the Doctor replies that it mustn’t. Taltalian is insisting to the Doctor that he is not trying to be obstructive when the telephone rings. Taltalian answers, but the caller wants to speak to the Doctor; they do not give their name, but threaten to kill Liz if the Doctor does not stop interfering. Having told Taltalian the gist of the call, the Doctor advances menacingly towards him - then stops and cheerfully suggests they get back to work.

‘Two million rads,’ reports Liz, seated at a computer panel in Lennox’s lab. ‘Dropping to two million minus fifty thousand.’ Lennox carefully writes this down. He glances round at the three ‘astronauts’, one of whom is slumped over, and tells Reegan’s thug (Will Masters) to tell Reegan there is only one canister of the isotope left. Masters appears reluctant to move. ‘Well? Do you want them to die?’ Lennox asks him, and Masters goes out of the lab. Liz hurries up the stairs to the other door, but finds it locked. She comes back down the stairs dejectedly. ‘Are you a prisoner?’ she asks Lennox. He is evasive, but she insists on an answer. ‘I can come and go as I please,’ he replies, ‘but I haven’t got anywhere to go.’ Liz reminds him that he was once a respected scientist. ‘Grossly underpaid!’ he retorts defensively. He asks for Liz’s help putting on the headgear of his radiation suit. He takes out a key and puts it down next to Liz. ‘I lost my key somewhere,’ he says meaningfully. ‘For that door up there.’ Tacitly he gives Liz her instructions: ‘They’ll find me in the cubicle. Locked and bolted from the outside, do you understand?’ Liz asks Lennox if he wants to go with her; but as he said, he has nowhere to go. She puts the protective headgear on him, and takes the key. Then she seals him into the cubicle with the ‘astronauts’, and heads for the way out.

The Doctor realises that the impulses are a mathematical formula for building an electronic device; he tells Taltalian that he will have to build the device to find out what it is. The Doctor seems unconcerned about the threat to Liz, because the people who made it will not know what he is up to - ‘unless somebody tells them’. ‘Who would do that?’ laughs Taltalian. ‘You, for instance?’ suggests the Doctor.

Liz creeps out of a back door of the laboratory building, and has a good look around before running away.

Taltalian accuses the Doctor of being ‘most insulting’; the Doctor accuses him of being ‘continually obstructive’. Taltalian claims again to have been merely acting under General Carrington’s instructions, but the Doctor wonders whether Taltalian could be involved with the people who are really behind the plot: ‘the people who kidnapped Miss Shaw, who kidnapped the three astronauts’. The Doctor tells Taltalian that he has not shared his suspicions with the Brigadier because he has an alternative to offer to him. He stares at him and sets out the two options: ‘A ruthless investigation by the Brigadier, or a few quiet words with me and your name kept out of things.’ ‘I don’t know what you are talking about,’ says Taltalian. ‘I think you do, Taltalian. And I’m going to give you a little time to think it over.’ The Doctor leaves the room to see about building the machine, telling Taltalian to think over what he has said. Left alone, Taltalian goes to a cupboard and takes out a small electronic device.

The fleeing Liz arrives at a country road. The first car she tries to flag down fails to stop for her. The second car does, but its driver is Taltalian. He pulls a gun on her and tells her to get in. She does so, and they drive away.

Back at Lennox’s laboratory, Liz protects Lennox by telling Reegan that no one helped her to escape; ‘that door was left open,’ she says. Reegan points out that she might have killed Lennox by locking him in with ‘those things’, but Liz pretends not to care. Reegan orders her back to work with Lennox, and Masters gives her a shove to help her on her way. Reegan tells Masters to make sure the door is kept locked. Taltalian gives Reegan the electronic device, together with operating instructions and the communication code. Reegan is suspicious that it seems ‘a little too simple’; ‘I need to talk to those things,’ he tells Taltalian. ‘You have a list of simple signals and commands,’ Taltalian replies. ‘Transmit and they will obey.’ ‘And if they don’t?’ ‘You threaten to cut off their supply of radiation - there is a signal for that too.’ Taltalian confirms that there is also a machine for translating the replies, but it is in his computer room, and Reegan will not need it. ‘I’m the one dealing with these creatures,’ Reegan points out. ‘You will use these creatures to carry out a series of raids on carefully chosen targets,’ says Taltalian. ‘You know enough to do your job, but I have further instructions for you….your call to the Doctor threatening the girl’s life was stupid,’ he adds. Far from slowing the Doctor down, ‘it merely made him more determined and suspicious - suspicious of me.’ ‘Too bad,’ Reegan replies. Taltalian says that the Doctor has to be ‘put out of the way permanently’; he is about to discover how to build another machine of the type Taltalian just gave Reegan. Reegan agrees to deal with the Doctor. ‘And since your own skin’s in danger,’ he tells Taltalian, ‘you can help me.’

‘Taltalian - do you have any proof?’ the Brigadier asks the Doctor. ‘No, not a scrap,’ confesses the Doctor, drinking his cup of tea. ‘Then why accuse him?’ The Doctor attributes it to intuition, something even Taltalian’s computers don’t have. The Brigadier reminds the Doctor that Taltalian was acting under Carrington’s orders, as Quinlan explained. The Doctor remembers, but is completely unconvinced: ‘First they try keeping us in the dark altogether, and when that didn’t work, they fall back on some prepared cover story - contagious radiation indeed!’ The Doctor does not know what is going on, but thinks he might know more after having built the device. He shows the Brigadier a list of the advanced electronic equipment he needs to make it, and says he needs the equipment at once; the Brigadier agrees to see to it. On his way out to his laboratory, the Doctor asks the Brigadier if there is any news of Liz, but there is not. ‘We’re doing all we can,’ the Brigadier assures him.

Lennox whispers his thanks to Liz for keeping quiet about his role in her earlier escape. She is clearly developing a new escape plan: ‘If at first you don’t succeed…’ Lennox tells her she will not get another chance. ‘We’ll see,’ she replies. He asks how Liz was caught. ‘I ran into an old friend,’ she tells him.

Reegan joins Taltalian, who insists impatiently that he has to get back. ‘It’s a delicate operation,’ Reegan tells him. He shows Taltalian the interior of a briefcase, which contains a bomb. ‘It’s quite simple. All you have to do is set the dial to the time you require. How long do you need to get clear of the building?’ ‘Ten minutes, maybe more.’ ‘Let’s say quarter of an hour,’ says Reegan. ‘We can’t have you taking risks.’ He sets the dials accordingly and closes the briefcase. ‘Now, you leave the case as near to the Doctor as you possibly can. You slide these catches together, and that starts the mechanism. Fifteen minutes later - no more Doctor.’ Reegan explains that if the Doctor tries to open the case ahead of time, the result will be the same, just a little earlier. Taltalian is concerned about the risk, but Reegan reminds him that it is him the Doctor is after. While Masters helps Taltalian on with his coat, Reegan - unseen by Taltalian - opens the briefcase and makes a quick adjustment to the dials inside, then closes the briefcase again. He hands the case to Taltalian, who takes it carefully. ‘Do as you’re told,’ Reegan tells him, ‘and your troubles will be over.’

Cornish is complaining to the Doctor about the sudden suspicious lack of available astronauts. A variety of excuses has been given: ‘not fit; transferred to other duties; waiting for security clearance.’ ‘Is that all?’ asks the Doctor, and he offers to take the rocket up himself. Cornish thanks him, but suggests the Doctor does not realise what this would entail. ‘My dear man,’ replies the Doctor, ‘I’ve spent more time in space than any astronaut on your staff - not, I’ll admit, in the rather primitive contraptions that you use, but I’ll manage…I can also withstand considerably more G-force than most people, even though I do say so myself.’ Cornish accepts. The Doctor will have to take certain tests, but he readily agrees to this: ‘When that recovery capsule is ready, I’ll take it up.’

Taltalian now comes in, with the briefcase, to join the Doctor and Cornish. He tells Cornish that he has the computations for lift-off, all but the final phase. Cornish asks Taltalian to let him have them as soon as possible, and leaves to see about the tests the Doctor will have to take. A tense atmosphere reigns once Taltalian and the Doctor are left alone. Taltalian goes to the cupboard. The Doctor asks him if he has thought over what he spoke to him about. ‘I will tell you everything,’ Taltalian says, ‘if you will give me a chance to get away.’ The Doctor agrees to this. Taltalian goes across to the briefcase, which lies flat on a work-surface a few feet away from the Doctor. He tells the Doctor that the information he needs is in his car, and that he will go and fetch it; ‘you will wait for me here?’ The Doctor agrees. Taltalian has a nervous look across at the Doctor, and slides the catches on the briefcase - which immediately explodes in his face. Taltalian recoils with a horrible scream.

At Lennox’s laboratory, Liz believes she has got the communication device to work. Reegan tells her to send the signal ‘stand up’, and she does so; behind the transparent screen, the three space-suited figures get to their feet. Liz sends the signal ‘forward’, and each figure moves slowly forward. ‘Send “stop”,’ says Reegan, and again the three captives silently obey. Liz tells Reegan that the device might be simple enough for even him to be able to use it. He takes the device. Liz asks Reegan about the briefcase he gave to Taltalian. ‘You could say it was a way of killing two birds with one stone,’ he replies.

In the smoky, bomb-damaged computer room, the Brigadier concedes to the Doctor that he seems to have been right about Taltalian. ‘Lot of good it did me - and him,’ says the Doctor. Taltalian having been killed by the full force of the blast, the Doctor has escaped with a minor facial injury; there is a dressing on his right cheek. The Brigadier assumes that the mechanism of the time-bomb was faulty, but the Doctor is not sure that it was: the remains of the mechanism show that the timer was set to zero, so that the bomb would go off instantaneously. ‘So whoever gave it to him wanted to get rid of both of you,’ says the Brigadier. The Doctor concludes that Taltalian was a weak link, whose employers wanted him out of the way - it seems like another dead end. The Doctor finds, in Taltalian’s cupboard, a small device very similar to the one he is trying to build: ‘Taltalian had one all the time.’

Quinlan tells Carrington that time is running out: the new recovery rocket is almost ready to go up. ‘You were supposed to stop him, sir,’ says Carrington. But Quinlan has tried every possible delay, and now the Doctor has even volunteered to pilot the rocket. ‘He must be stopped,’ Carrington tells Quinlan. Quinlan suggests telling him the truth, but Carrington says that they know too little about him. ‘There may be no alternative,’ Quinlan replies. ‘There’s got to be,’ says Carrington. ‘If that rocket goes up, it means disaster for the entire world.’

With his feet up on the desk in Lennox’s laboratory, Reegan is talking on the telephone, assuring a superior that everything is going fine, but expressing his regret that the Doctor survived the bomb: ‘This Doctor fellow must have nine lives.’ He agrees to organise a mysterious something ‘tonight’. He instructs Masters to go and get the van, and tells Lennox that their three captives are going on ‘a little excursion’. A reluctant Lennox opens the door to the captives’ area of the laboratory. Reegan asks Liz if the communication device can work the other way round, so that the three captives can talk to them; she says no, but confirms that there could be a machine to perform this reverse function. ‘I think I’ll be paying two visits tonight,’ Reegan says thoughtfully. He uses the signalling device, and the figure clad in Van Lyden’s space suit emerges into the main part of the lab.

A short while later, in the dazzling light of the setting sun, the space-suited figure approaches the perimeter of the Space Centre complex. A UNIT soldier on guard duty shouts to the approaching figure to halt. It ignores this, and a second shout of ‘Halt or I’ll fire!’ The soldier fires six bullets from his handgun at the approaching figure, with no effect. It arrives at the perimeter barrier and takes hold of it; a wave of energy races along the length of the barrier and kills the soldier at the other end. The creature in Van Lyden’s space suit lifts the barrier and continues its remorseless approach into the complex.

Inside, the creature arrives in the computer room, where two scientists are working. A touch of its left hand kills the younger scientist in a sizzling blast of energy; the older man tries to put up a fight but is felled in the same way. The intruder advances to the cupboard and reaches inside it. A UNIT soldier appears in the doorway with a much more substantial gun than the perimeter guard’s; but this too is ineffective against the creature, which kills him with a touch to the neck.

‘I tell you it converts radio impulses into human speech,’ the Doctor is explaining to the Brigadier. ‘The aliens in Heldorf’s laboratory were trying to communicate with him.’ ‘So you were right,’ says the Brigadier, ‘they aren’t human.’ ‘I never believed they were,’ says the Doctor. He would now like to build the other half of the device in order to be able to contact the creatures, but the electronic parts that he ordered are taking a while to arrive, most of them needing to come from Japan. Quinlan telephones the Doctor to ask him if he still intends to pilot the recovery rocket; he does. ‘I can’t persuade you that your action will be disastrous?’ asks Quinlan. ‘You might,’ replies the Doctor, ‘if you were to tell me the truth, Sir James - the whole truth.’ Left with no choice, Quinlan invites the Doctor to come to see him at once. The Brigadier is keen to accompany the Doctor.

The Doctor sees the creature bearing down on him, but it is too late to move out of the way. He remains lying across Quinlan’s body as the creature’s hand reaches slowly for his face. But the Brigadier has appeared in the doorway of the office; he draws his gun and fires at the space-suited figure. The Doctor yells to the Brigadier to stop, but the Brigadier has saved his life - the creature turns away from the Doctor without making contact with him. It starts to head for the doorway, and the Doctor warns the Brigadier not to try to stop it. A UNIT soldier rushes in, and the Doctor’s warning comes too late - the space-suited figure brushes the soldier aside, killing him instantly, and then walks out of the office, closing the door behind it. The lock mechanism bursts into flames, sealing the door shut. The Brigadier tries the door handle in vain. ‘No, there’s no point in trying to follow him,’ says the Doctor. ‘There’s nothing we can do.’

‘Do you really think they’re not human?’ Lennox asks Liz. This is what she wants to find out. She asks where Reegan has taken the third creature. Lennox says he does not know, and tells her not to ask so many questions. But she asks one more: ‘Is Reegan in charge?’ Lennox says no; Reegan works for ‘someone high up’. Liz says that Reegan has to be stopped. ‘You won’t get away again,’ warns Lennox. ‘But you might,’ she replies.

In Quinlan’s office, the Brigadier shows the Doctor the bullets that have been fired at the intruder; they have been flattened by the impact. ‘Deflected by some kind of force field, I should think,’ the Doctor surmises. ‘So there’s no way of stopping them,’ says the Brigadier. ‘Not with bullets,’ replies the Doctor, as if this should have been obvious. Benton (last seen in The Invasion) comes in to report that there is a strong radioactive trace as far as the road outside, and then nothing. Clearly the creatures were taken away in a vehicle. ‘Somebody’s using these creatures, Brigadier,’ the Doctor says. ‘They’re not free agents. They were brought to Earth for some purpose.’ ‘Conquest?’ asks the Brigadier. ‘Possibly,’ says the Doctor. ‘Or is that what we are supposed to think?’

Controlled by Reegan’s signalling device, the creature in Van Lyden’s space suit descends the stairs into Lennox’s laboratory.

At the Space Centre, Cornish tells the Doctor that for the first two and a half minutes, the rate of fuel consumption will be fifteen tons per second. The mixture of standard fuel and M3 variant that they are going to use has never been tried before, but enough of the standard fuel will not be available in time. Quinlan’s death has made things harder, not easier: ‘everything’s wrapped up in red tape until they appoint a successor,’ says Cornish. Cornish has the Doctor’s medical report, which he describes as ‘incredible’. The Doctor forestalls any awkward questions about his non-human physiology with bluster: ‘I told you everything’d be all right.’

In the sealed-off section of Lennox’s laboratory, the space-suited creature which has just returned collapses to the floor, but Lennox, dressed in his protective suit, is there to fortify it with radioactive isotope. Lennox emerges into the main part of the lab. Liz asks Reegan what he has done to the creature. ‘It’s had a busy time,’ Reegan replies. ‘Busy?’ asks Lennox. ‘Doing what?’ ‘Killing,’ says Reegan. He tells Liz that some of her friends from UNIT were among the targets - not the Brigadier, just some of the other ranks. ‘One touch from him, and down they go,’ says Reegan delightedly. Liz expresses surprise that no one resisted. ‘They tried,’ Reegan says. ‘Bullets just bounce off them. With these three you can do anything - walk into Fort Knox and help yourself.’ Liz asks if that is what he intends to do with the creatures. ‘I might,’ he replies. ‘Keep feeding them radiation, I’ve got a lot more work for him to do.’ He leaves, telling his thug Tony (Flynn) to lock the main door at the top of the stairs and then confirm sealing. ‘You’re working for a murderer,’ Liz tells Lennox. Lennox dismisses Reegan’s statements as mere boasting, but Liz knows he does not believe this. ‘Look it’s got nothing to do with me, Miss Shaw! I’m paid to look after them!’ ‘You are just as guilty as if you’d killed those people yourself,’ Liz insists. She asks Lennox what he is going to do about it, but he says he is too much involved to do anything. She says he could go to UNIT and tell them the location of the lab - the Brigadier will give him protective custody. Lennox points out that he cannot leave anyway, because Reegan has taken his key to the door. ‘Then you’ll just have to talk your way out,’ says Liz.

At the Space Centre, General Carrington tells the Doctor and Cornish that he absolutely forbids the new rocket launch. Cornish tells Carrington that he does not have the authority to forbid it. ‘What have you got against it?’ asks the Doctor. ‘Sir James Quinlan murdered,’ replies Carrington. ‘Alien creatures attacking the Space Centre. The sudden death of Doctor Taltalian. This is obviously just the beginning.’ ‘The beginning of what?’ asks Cornish. ‘An alien invasion with the collaboration of a foreign power.’ The Doctor suggests that this is all the more reason for him to make the trip. Carrington now questions the use of the Doctor as an astronaut, but the Doctor is insistent on knowing why Carrington is opposed to the launch. The General believes that the rocket should be used to carry a nuclear warhead rather than the Doctor. ‘Since we don’t know what’s up there, wouldn’t it be more intelligent to carry a man rather than a bomb?’ the Doctor asks. Carrington points out that he is responsible for space security, but Cornish points out that he is responsible for the Space Centre. Carrington reminds them that the launch was against Quinlan’s wishes; the Doctor suggests that the General take the matter up with Quinlan’s successor - ‘when he’s been appointed’. ‘I shall go to the highest authority to have you stopped,’ warns Carrington. ‘Then you’d better get on with it, General,’ replies Cornish, unruffled. ‘We blast off in two hours’ time.’

The collapsed space-suited creature in Lennox’s laboratory is recovering. Liz tells Lennox that he is the only one who can stop Reegan ordering more murders: she wants him to make a telephone call, but Lennox points out that all the calls are monitored. ‘Then you’ll have to go yourself,’ she says. The thug Flynn returns. In a hushed voice, Liz tells Lennox to demand to see Reegan on the pretext that more isotopes are needed. After some initial reluctance, Lennox tells Flynn that he needs to see Reegan urgently. Flynn is uninterested, saying that Reegan is in London having ‘a meeting with the boss’. Liz says the creatures are dying. Flynn looks through the transparent screen at the figures, which are all standing. ‘How can you tell?’ he asks. Liz directs him to the readings on the computer console. Flynn, of course, has no idea what he is looking for. Lennox points to a dial and says it should be at maximum, then says he needs to go and get more isotopes. ‘No one is to leave here,’ Flynn says. ‘Then you’ll be responsible if they die,’ replies Liz. She and Lennox tell Flynn that there is no time to telephone Reegan - Lennox must leave immediately. Lennox says he is not a prisoner; Reegan took his key because Liz tried to escape: ‘You’re supposed to be guarding her, not me.’ He orders Flynn to open the door, and Flynn does so. On his way out Lennox adds a touch of realism by telling Flynn to keep an eye on Liz. This makes her smile.

A female control room assistant at the Space Centre reports that forty per cent of fuel is now loaded into the rocket that will carry the Doctor into space; ‘will switch to M3 variant at sixty-five per cent,’ she adds. Cornish acknowledges the fuel injection report with his usual stoic calm. Everything is in ‘go’ condition. Cornish tells the Doctor that it is time he was in the preparation room. The Doctor explains to the Brigadier that the lift-off time has been advanced because of official opposition to the mission. The Brigadier is interested to learn that Carrington is trying to prevent the launch. The Doctor sets off for the preparation chamber. Sergeant Benton telephones the Brigadier to report the unexpected arrival of Lennox, who seems very agitated. Lennox has said that he knows something about the missing astronauts, but has insisted on speaking only to the Brigadier in person. Benton reports that Lennox ‘seems frightened - scared out of his wits’. He has requested protective custody. The Brigadier tells Benton to put Lennox into one of the cells, and says that he will be back to see Lennox as soon as possible, when he has finished his security checks.

Benton shows Lennox into a cell. ‘You can’t be safer than in a cell,’ Benton explains gently. He asks Lennox what he is so frightened of, but Lennox repeats that he can speak only to the Brigadier. Benton offers Lennox a cup of tea and something to read, but he declines, asking Benton to lock the door on his way out. Puzzled, Benton does so.

The female control room assistant reports to Cornish that the Doctor is now ready and is proceeding through the quarantine area to the Recovery Seven capsule. The Brigadier is waiting to see the Doctor off when the Doctor walks in, wearing a space suit minus helmet and gloves. The Doctor finds the ‘waiting room’ rather unimpressive for one’s last sight of Earth. The control room assistant’s voice instructs the Doctor to proceed to the capsule, and the Brigadier wishes the Doctor good luck and shakes his hand. The Doctor leaves through sliding double-doors like those of a lift.

Reegan is reprimanding Flynn for letting Lennox leave the laboratory. In his defence, Flynn explains that both Lennox and Liz told him the creatures were dying. ‘So you put him up to this,’ Reegan says angrily to Liz, and grabs her arm roughly. ‘There’s nothing wrong with them.’ Liz sticks to the story that Lennox has gone for more isotopes. ‘You’re lying,’ says Reegan, pulling out his handgun. ‘Did you send him to see your friends at UNIT, is that it? Answer me!’ With Reegan’s gun jammed against her chin, Liz confesses that Lennox has gone to see the Brigadier. ‘You’re too late,’ she tells him. ‘Don’t you believe it,’ retorts Reegan, and shoves her across to Flynn. Flynn orders Liz not to try anything. ‘It’s all right, I won’t hurt you,’ she tells the huge man. Reegan gets on the telephone and requests a direct line. He tells whoever is on the other end that Lennox has gone to UNIT. ‘All right,’ he agrees, ‘you take care of Lennox and I’ll take care of the Doctor.’

Fifty per cent of the fuel is now loaded. Cornish asks the Doctor, who is now installed in the capsule, if he has completed his instrument check. ‘Everything seems to be working all right,’ confirms the Doctor. Thirty minutes remain before lift-off. The Doctor asks if fuel injection can be hurried up, but Cornish says no because the M3 variant is highly volatile. The Doctor still believes a higher proportion of M3 could be added: ‘And remember, the extra G-force wouldn’t worry me.’ But Cornish is more concerned about the risk of the rocket exploding on lift-off: ‘I’m not taking the risk,’ he says.

Near a notice reading ‘Space Control Centre/Fuel Bay/No Smoking/No Naked Lights/Danger’, a UNIT soldier quizzes Reegan, who has turned up in workman’s clothes claiming to have been requested to do some work. The soldier asks to see Reegan’s pass. Reegan gives him something to read, but then quickly doubles him up with a punch to the stomach, and then carries the prone soldier swiftly out of sight. Reegan climbs up a ladder amidst a vast structure of piping and metal. Spotting a technician at work, he inches down towards him and kicks him off the structure. Reegan races up steps, higher and higher in the structure. He adjusts a control on a pipe and hurries away, leaving steam pouring out of the sabotaged mechanism.

A male control room assistant reports to Cornish that life support systems are at go. But the female assistant announces that there is a fuel injection malfunction. Cornish anxiously orders the Fuel Bay staff to check all fuel injection circuits; but he allows his voice to betray none of his anxiety as he reports the situation to the waiting Doctor. The female assistant states that the fuel injection systems are now functioning normally, and Cornish passes this on to the Doctor.

Reegan is still making his escape. He encounters another member of the Space Centre’s staff but quickly floors him with a two-footed kick, using the railing for support. He turns various valves to deliver too much M3 variant into the mixture of fuels. Then he races away down the steps.

Lennox is snoozing in his cell when someone comes in with a tray: ‘I’ve brought you some food.’ Lennox thanks him. He asks his visitor to lock the door on his way out, and the visitor does so. Left alone, Lennox removes the cover from his plate and sees with horror that instead of food, he has been given a radioactive isotope cylinder - and he is trapped in the room with it.

The Brigadier drives into the Space Centre complex in a UNIT land-rover. The soldier who was attacked by Reegan tells the Brigadier that his assailant went to the fuel bay. The Brigadier gets out of the land-rover and heads for the fuel bay, where he sees the outpouring of steam resulting from Reegan’s sabotage.

‘Final check completed,’ reports the female control room assistant. ‘All systems now go.’ Cornish checks that the Doctor is all set, and announces lift-off in fifteen seconds. ‘About time too,’ says the Doctor. The male assistant begins the final countdown from ten. At ‘four’ the Brigadier races into the control room and tells Cornish he must stop the countdown, but it is too late - the count reaches zero and the rocket lifts off. The rocket soars up through the atmosphere. In the capsule, the Doctor’s face is distorted by the enormous G-force. ‘Lift-off speed twenty per cent in excess and rising,’ reports the female assistant. The fuel burn rate cannot be reduced from a highly dangerous forty-eight per cent. ‘Reduce flame apertures,’ orders Cornish. If something is not done quickly, the Doctor risks blowing himself out of Earth’s orbit and going into the sun. ‘Apertures will not close on automatic owing to excessive heat,’ says the female assistant. ‘Lift-off speed now thirty per cent in excess.’ Cornish tells the Doctor to operate the flame apertures manually to reduce his speed. Pinned agonisingly into his seat by the G-force, the Doctor says he will try. The lift-off speed is now thirty-seven per cent in excess, and the computer calculates the capsule will go into the sun’s orbit in fifteen minutes. The controls do not respond to the Doctor; he recommends that Cornish jettison Stage One prematurely. ‘If we do that you may never get into orbit at all,’ replies Cornish. But the Doctor insists: the excessive momentum from jettisoning Stage One may put him into Earth’s orbit, and anything is better than going into orbit around the sun. So Cornish gives the order, and Stage One is jettisoned, exploding immediately after separation. The Doctor, relieved of the crushing pressure of the G-force, thanks Cornish. The rocket’s speed reduces to normal. The Doctor asks Cornish what went wrong, and the Professor tells him it was sabotage. ‘They’re very persistent, aren’t they?’ says the Doctor. Stage Two is jettisoned. A thirty-second burn on the Stage Three rocket will now put the Doctor into Earth’s orbit.

The Doctor cannot see Mars Probe Seven yet. However, he is within half a mile of the probe, and converging with it. Cornish tells the Doctor to change the attitude of the capsule three degrees starboard; the Doctor, unfamiliar with such a primitive space vehicle, takes a moment to comply. The Doctor sees Mars Probe Seven, and starts to manoeuvre Recovery Seven to link up with it. He completes the manoeuvre beautifully. ‘Moving through into Mars Probe Seven now,’ reports the Doctor, and unclips himself from his seat. ‘Doctor, be careful,’ warns Cornish. ‘We don’t really know what’s in there.’ ‘Nonsense man, your three astronauts are in there.’ The Doctor operates a control to eject air into the tunnel between the two spacecraft.

The Doctor tells Cornish that the object is an enormous spaceship. The Doctor sets about trying to evade collision, but Cornish and the Brigadier, watching the two blobs of light approaching each other on their monitor screen at the Space Centre, see that he does not have the speed necessary to avoid the huge ship; Recovery Seven is hampered by being still linked to Mars Probe Seven. Furthermore, the Doctor has precious little fuel to execute the manoeuvre, and what he has he will need for re-entry. ‘It’s closing in too fast!’ exclaims the Doctor’s voice from a speaker. ‘I can’t - ’ Then radio contact is lost. On the monitor screen, the two blobs of light converge and the smaller one disappears. ‘They’ve collided,’ says the Brigadier to Cornish. ‘If they had, the capsules would be smashed to fragments,’ Cornish replies.

As the Doctor lies back in his seat in Recovery Seven, a bizarre, harsh alien voice tells him: ‘You are not in danger.’ He asks where he is. ‘You are on board our spacecraft,’ says the voice. ‘Open your hatch and leave the capsule.’ The Doctor asks what has happened to the three astronauts. The voice tells him they are unharmed, and repeats its instruction to open the hatch and leave the capsule. The Doctor agrees and picks up his space helmet, but the voice tells him he will not need his life support systems: ‘An environment has been prepared for you.’

The Recovery Seven capsule materialises in a vast glowing tunnel. The Doctor opens the hatch and leaves the capsule, then drifts to the tunnel floor in apparently reduced gravity. ‘Go to the light,’ the voice instructs him, and the Doctor starts to make his way towards the light at the end of the tunnel.

The three astronauts, Van Lyden, Michaels and Lefee, are seated around a futuristic oval device. Its screen shows only patterns of light, but the three men appear to believe they are watching a football match, cheerfully arguing about the progress of the game. The Doctor walks in. ‘Do you happen to know how long we’re going to be kept here?’ Lefee asks him urbanely. ‘What are you talking about?’ asks the Doctor. Lefee is puzzled by this, and asks for the device they think is a television to be turned off - their team is losing anyway. Michaels switches it off. Van Lyden asks the Doctor if he knows when they are going to see their families. The Doctor looks at him thoughtfully, then asks: ‘Do you know where you are?’ Van Lyden is bemused, and the Doctor has to repeat the question. ‘Yes of course,’ says Van Lyden. ‘I brought these two fellows back from Mars Probe Seven, they slapped us in extended quarantine.’ ‘You think you’re on Earth - at the Space Centre?’ asks the Doctor, surprised. This is greeted with laughter. ‘What do you think that is?’ asks Lefee, pointing as if out of a window. Michaels asks the Doctor what he wants. ‘I came to take you back to Earth,’ says the Doctor. The astronauts treat this as a joke. ‘Now please, listen to me,’ the Doctor tries to explain. ‘You’re not on Earth, nor are you at the Space Centre. You’re prisoners in an alien spaceship.’ He tells Van Lyden: ‘You came up here in Recovery Seven but you never made the journey back. Something happened.’

At this point a high-pitched hypnotic sound issues from the oval device, and the three men sit back down in a kind of trance. The Doctor snaps his fingers in front of Michaels’ face and passes his hand in front of Van Lyden’s, without effect. ‘They cannot hear you,’ says the alien voice; the voice’s owner is now seen, though rather indistinctly, on a large monitor screen. ‘You’ve conditioned their minds,’ says the Doctor reproachfully. ‘It was necessary for their health,’ states the alien, making peculiar gestures with its arms. ‘They were deteriorating.’ The Doctor asks why the astronauts have been taken prisoner. The creature answers his question with another: ‘Why have you not returned our ambassadors?’ ‘Ambassadors?’ asks the Doctor. ‘An agreement was made. You have betrayed us. Unless our ambassadors are returned, we shall destroy your world.’ ‘Ambassadors!’ breathes the Doctor, as everything finally falls into place for him.

At the Space Centre, the female control room assistant has received information from Jodrell Bank that the spaceship is discoid and half a mile in diameter. The Brigadier thinks that such a large object must be a meteor, but Cornish knows that meteors do not stand still. General Carrington is also present; he says that the object is obviously an alien spacecraft, and must be attacked and destroyed. The Brigadier is concerned for the Doctor, but Carrington’s argument is that he must be dead by now anyway. ‘We could use missiles with atomic warheads,’ he says. Cornish objects, but for the General the matter is closed. ‘I’ve got a plane to catch,’ he says. ‘There’s an emergency meeting of the Security Council in Geneva in an hour’s time.’ The object has been spotted by observers all over the world, and the General intends to recommend an immediate all-out attack on it: ‘We must defend ourselves while there is still time.’ ‘The man’s mad,’ remarks Cornish after Carrington’s departure. ‘Not necessarily,’ says the Brigadier. ‘We don’t know what that thing is there.’ Cornish is in favour of finding out, but the Brigadier believes that someone may have found out already: ‘I have a feeling that General Carrington knows a great deal more than he’s telling us. He went on a Mars probe himself, remember. Perhaps he discovered something.’ The Brigadier definitely does not support Carrington’s plan to attack blindly: ‘I think we should wait. But there’s only one hope left to us - that the Doctor is still alive.’

‘What you tell me is appalling,’ says the Doctor to the alien on the screen. ‘The authorities on Earth had no knowledge of this.’ ‘That is difficult to believe,’ replies the creature. ‘Nevertheless, you must believe me. Now let me go back to Earth, and I will give you my personal assurance that your ambassadors will be returned to you.’ ‘But you do not even know where they are.’ ‘From the information that you’ve given me, I’ll find them,’ says the Doctor. ‘Now please, you must let me try.’ ‘Very well. But if our ambassadors are not returned, we shall use our weapons to destroy your world.’ ‘These three men - can I take them back with me?’ ‘They will remain here until our ambassadors are returned. Now you can go back to your spaceship.’ The image of the alien fades from the screen.

The hypnotic sound fades away and the three astronauts emerge from their trance. ‘Something happened?’ asks Van Lyden, carrying straight on from where his earlier conversation with the Doctor left off. ‘Yes,’ says the Doctor. Playing along with the illusion, he tells the men that he will see what he can do about getting them out of quarantine as soon as he possibly can. They seem pleased about this. Michaels asks the Doctor to send something in for them to read. The Doctor leaves, and they turn the oval device back on to catch the end of the football game: ‘That’s better, one all!’

‘The American Space Agency are now preparing to launch an unmanned capsule to observe the unidentified object,’ reports the female control room assistant. The male assistant reports that radio pulses have been detected being emitted by the object at a frequency similar to those emitted by pulsars. The American unmanned capsule will be launched in an estimated six hours. The Brigadier returns with the news that Lennox has been murdered. ‘In your own headquarters?’ asks Cornish incredulously. ‘Someone put an isotope in his cell,’ says the Brigadier. The Brigadier concedes that he is not having a great deal of success. ‘The astronauts are still missing,’ Cornish points out. ‘Miss Shaw kidnapped. Doctor Taltalian killed. And now this man Lennox murdered under your very nose.’ However, UNIT has identified the two radioactive bodies that were found in the gravel pit in Hertfordshire: they were not foreign agents, but petty London criminals. The Brigadier also now knows that the explosive which killed Taltalian was ‘the new H37 compound, which hasn’t even been issued to the army yet.’ ‘Then our own people could be involved,’ Cornish concludes. ‘That was the Doctor’s theory,’ says the Brigadier. In addition, forensics have found elements of insecticide in the mud on Lennox’s shoes, indicating where he might have been recently; UNIT is now checking all the areas where this insecticide is used. The isotope that killed Lennox was part of a consignment sold some months ago to ‘a bogus company with an address that doesn’t even exist.’ Cornish congratulates the Brigadier on the thoroughness of his investigations, but the Brigadier is aware that they do not seem to have got him anywhere.

The radio pulses being emitted by the alien spaceship have now ceased. On the monitor screen, two blobs of light are again visible, indicating the departure of Recovery Seven from the alien ship. The Doctor re-establishes contact with Space Control, and his image appears on the huge wall-screen. The Doctor confirms that he is all right, and reports to Cornish that the astronauts are safe and well. ‘I’m not going to say any more at the moment, it’s not safe…I shall maintain radio silence until the necessary landing instructions.’ He tells the Brigadier to put all his men on standby, and says he will explain everything when he lands. Cornish wants to know what happened to his astronauts, but the Doctor is saying nothing more for the moment. The Brigadier advises Cornish that he is wasting his time pressing the Doctor to talk before he wants to, and says he must get on to UNIT headquarters. Recovery Seven is now approaching re-entry orbit.

In the protected section of the laboratory of the late Doctor Lennox, Liz is providing the space-suited aliens with isotope. She gets up to leave and one of the aliens blocks her way; another slowly removes its helmet. Its face is nightmarishly hideous, wide and lumpy and all the more grotesque by being framed by human-like hair. Liz, utterly terrified, beats against the transparent screen of this section of the lab, apparently not realising in her panic that she can simply run out of the door and into the main part of the lab - which she then does. Shaken, she starts removing her protective headgear. Reegan returns to the lab and sees the state Liz is in: ‘What’s the matter with you?’ ‘Look!’ she replies simply, and points at the creature behind the screen. ‘Ugly looking fellow isn’t he?’ Reegan observes nonchalantly. ‘You knew they weren’t human,’ says Liz. She asks him why he has got them here. He answers that he was paid to, but says it doesn’t matter by whom; he has a few ideas of his own, such as committing any robbery he likes. ‘Is that what this boss of yours wants you to do?’ asks Liz. ‘Doesn’t matter what he likes,’ says Reegan. ‘We’ve got them.’ ‘We?’ Liz asks. ‘There’s a vacancy,’ Reegan tells her. ‘Doctor Lennox met with an accident at Headquarters.’ ‘You killed him,’ says Liz furiously. ‘I never laid a finger on him,’ Reegan replies. ‘Well?’ he asks her. ‘Are you offering me a job?’ she asks in disbelief. He tells her that the alternative is that he kills her and buys himself another scientist. The telephone rings and he picks it up. ‘Oh it’s you sir,’ he says. ‘Doctor’s on his way down, is he? I did my best to stop him going up. You’re sure you want him dead? He could be useful to us. All right. I’ll see to him.’ He puts the telephone down. ‘Your friend the Doctor’s on his way back from a little journey. I’m going to be his reception committee.’

At the Space Centre, the Doctor’s perfect descent to Earth is being monitored; he is due to land in four and a half minutes. The Brigadier wants to go and meet the Doctor, and is alarmed to hear from Cornish that the Doctor’s decontamination will take not much less than an hour. ‘Think yourself lucky,’ says Cornish. ‘Used to take two days.’ The Doctor’s drop-speed reduces to twenty-two miles per hour, then eighteen; his height is one mile, with a drift rate of three knots and still on course. Radar contact is lost, and the capsule approaches the touchdown pad.

Reegan drives into the Space Centre Complex in the ‘Silcock Bakeries’ van, getting past the UNIT sentry at the main gate by showing him a pass.

The capsule touches down, and Cornish orders its parachutes disconnected.

Reegan parks near a sign reading ‘Decontamination Unit Ventilation System’. He unpacks a length of tube attached to a machine in the back of the van, and takes the other end up to the pipe system that ventilates the Decontamination Unit. He starts to undo a nut with a spanner.

The Doctor’s entry to the Decontamination Unit is announced. Cornish tells the Brigadier he can relax.

The Doctor comes into the Decontamination Unit wearing a striped dressing-gown, and prepares to get dressed.

Outside, Reegan hurries back to the van, and turns the handle that will feed gas into the Decontamination Unit.

The Doctor, now fully dressed, hangs up the dressing-gown and announces into a microphone that he is ready to come out. Cornish tells him to stay where he is just a few minutes more, while the final test results are awaited. The Doctor agrees, then sits down, lies back and closes his eyes. Then he begins to cough, and is swiftly overcome by the gas pouring into the room through the ventilation system.

Reegan checks his watch and shuts the gas off again.

The Doctor is lying unconscious on the floor when Reegan comes in, wearing protective mask and glasses. He starts to pick the Doctor up.

All the decontamination tests have come up negative. Cornish tells the Doctor over the intercom that he is cleared, but receives no reply. The Brigadier tries, but receives no answer either, and he sets off for Decontamination.

Reegan drives away in the van.

The Brigadier finds the gas-filled room deserted. He uses the microphone to tell Cornish to seal off all the gates.

Reegan, in the disguised van, is cheerfully allowed out by the UNIT sentry at the main gate an instant before Cornish’s call arrives. Reegan grins as he drives away.

Carrington suggests that the Doctor might have left of his own accord rather than having been abducted; the gas cylinder linked to the ventilation system could be ‘a blind to make us think he’d been kidnapped.’ Cornish is as sceptical about this as the Brigadier, but Carrington points out that ‘all these troubles only started when this Doctor came on the scene.’ The Brigadier respectfully but firmly denies this. ‘He insists on going up in Recovery Seven,’ says Carrington. ‘Makes contact with the alien vessel. Then disappears as soon as he lands. Can you explain that?’ ‘Do you really think that the Doctor is one of the people behind all this?’ asks Cornish. Carrington asks Cornish what he knows about the Doctor. ‘Only that he’s an associate of the Brigadier,’ Cornish is forced to concede. ‘Well, Brigadier,’ asks Carrington, ‘where does this man come from?’ ‘That’s difficult to explain, sir.’ ‘How long have you known him?’ ‘Several years - on and off.’ ‘On and off!’ repeats Carrington scornfully. ‘What’s his job, exactly?’ ‘He’s given my organisation a great deal of help in the past,’ the Brigadier replies. ‘You’re being deliberately unhelpful, Brigadier!’ exclaims Carrington. ‘I intend to have this “Doctor” investigated!’ ‘We shall have to find him first, sir,’ replies the Brigadier drily. ‘The sooner you do that, the better,’ says the General. ‘If he has any explanation to offer as to what that object is, we need to know it at once. Contact me as soon as you find him.’ Cornish asks Carrington how the Security Council meeting in Geneva went. Carrington says it was a complete waste of time - the council members are still debating, when they should be arming every available missile with atomic warheads and blasting the object out of the skies. ‘Isn’t that a bit extreme?’ asks Cornish. ‘It’s our moral duty,’ says Carrington with absolute conviction, then turns and leaves. ‘I think the General’s a bit overwrought,’ the Brigadier remarks. ‘I think he’s insane,’ says Cornish.

‘No trouble at all,’ says Reegan into the telephone in Lennox’s lab, while the Doctor lies on the floor. ‘Your Doctor friend’s as dead as a doornail.’ He hangs up. ‘Why do you say he’s dead?’ asks Liz, kneeling by the Doctor. ‘Because it suits me,’ Reegan replies. ‘How is he?’ The Doctor is slowly coming round. ‘I’m none the better for your attentions,’ he answers. He is, however, delighted to see Liz. Liz tells the Doctor that she has not been hurt, although she doesn’t much care for the company. The Doctor sympathises. With Liz’s help, he gets to his feet. Fascinated, he sees the aliens behind the transparent screen. ‘Doctor, they’re a completely alien species,’ says Liz. He tells her he has been aboard their spaceship and talked to their captain. ‘How did you talk to them?’ asks Reegan. The Doctor says they have a kind of translation machine. ‘Like this?’ Reegan asks, and shows the Doctor the small translation device. ‘Oh no,’ says the Doctor. ‘No, that’s a much simpler model. That would only receive one-way signals.’ ‘Could you build me a better one, so I could really talk to them?’ ‘I dare say, if I had the proper equipment,’ the Doctor replies. The Doctor is surprised that Reegan expects him to help him. ‘It would keep you both alive,’ says Reegan. The Doctor says that he will need a lot of expensive equipment. Reegan tells him to make a list, and politely helps him into a chair so that he can start writing it. Reegan sets off up the steps leading to the door out of the lab. The Doctor doesn’t waste much time in getting up to make his escape, but Reegan has waited at the top of the steps to warn him not to try it. Reegan leaves.

‘What are you doing?’ asks Reegan, descending the steps into the laboratory. Carrington, keeping his gun trained on the Doctor, rebukes Reegan for disobeying his order to kill the Doctor. ‘I thought it was for the best,’ says Reegan. ‘You’re not paid to think, Reegan!’ barks the General. Reegan points out that only the Doctor can make a machine that will allow them to talk to the aliens; Reegan’s device only sends limited one-way signals. ‘Look, if I’m going to carry out your orders,’ Reegan explains to Carrington, ‘I’ll have to give them some pretty complicated information. Still, suit yourself. You want to kill him - kill him.’

After a pause, Carrington puts away his gun. ‘Could you make us a better machine?’ he asks the Doctor. ‘Given the necessary equipment, yes,’ the Doctor replies. ‘And you’re willing to help us?’ ‘Depends on what you’re trying to do.’ Liz steps in, anxious that the Doctor should not try to push his luck any further, but the Doctor silences her. ‘Well, General?’ he asks. ‘We must alert the world to the menace of an alien invasion,’ says Carrington. ‘When do you expect this invasion?’ asks the Doctor. ‘At any time,’ says Carrington. ‘They told me that their intentions were peaceful,’ says the Doctor, ‘that these three beings here were ambassadors.’ ‘Ambassadors!’ exclaims Carrington. ‘That was just to put us off our guard.’ ‘You’re convinced their intentions are hostile, then?’ ‘Why else should they invade the galaxy? They were on Mars before we were.’ ‘Oh,’ says the Doctor, and gets up from his chair. ‘So that’s when you met them. When you were on a previous Mars probe.’ ‘Yes,’ says Carrington grimly. ‘They killed Jim. Jim Daniels, fellow astronaut - simply by touching him.’ ‘Yes, but they didn’t know that their touch would kill human beings.’ ‘Now they’ve walked into my trap!’ Carrington declares. ‘I knew that once I got them here, I’d make them reveal their true natures.’ ‘So it was you who sent for those three ambassadors, was it?’ ‘And hired Reegan to kidnap them and use them as killers?’ adds Liz. ‘It was the only way to arouse public opinion,’ says the General. ‘Was Sir James Quinlan in on this?’ asks the Doctor. ‘No - he just wanted the political glory of being the first to arrange contact with an intelligent alien species. He didn’t know of my plan to save the world. He wouldn’t have understood.’ ‘And what about Van Lyden and the other astronauts - the human ones?’ asks Liz. ‘They didn’t know either,’ replies Carrington. ‘It was the only way.’ ‘Well,’ says the Doctor thoughtfully. ‘I must say, you’ve been very thorough, General.’ ‘It was the only way,’ insists Carrington. ‘You do understand that, don’t you Doctor?’ ‘Yes,’ says the Doctor gently. ‘Yes, I understand. You had to do what you had to do.’ ‘Exactly!’ says Carrington. ‘We must protect the world, it’s our moral duty. Will you help us?’ ‘Yes,’ says the Doctor. ‘Yes, I’ll build your machine for you.’ ‘Splendid!’ exclaims Carrington delightedly. ‘This man can be of use to us,’ he says to Reegan. ‘Give him everything he needs.’ Reegan agrees. ‘I’m going to take one of those creatures with me,’ says Carrington to Reegan. ‘I’ve brought a shielded van. Kindly ask one of them to come out.’

At the Space Centre, news arrives that the American Space Agency’s unmanned observation satellite is now within three miles of the UFO. Its cameras cannot provide a picture, however, because of the radio signals emitted by the object. The American Space Agency prepares to manoeuvre the satellite down to one mile from the alien ship.

Carrington tells Reegan that he is to raid a number of isotope stores. He hands Reegan the information he will need. ‘Just follow your orders,’ says the General fiercely, and heads out of the laboratory.

The American observation satellite is no longer sending any signals, and is thought to have disintegrated. The Brigadier is informed over the telephone that Carrington’s men have captured an alien astronaut. ‘He’s going to bring it here,’ the Brigadier tells Cornish.

Reegan comes back into the laboratory with a henchman, and asks the Doctor how long it is going to take to build the communication device. ‘Look - I’m not building a crystal set you know,’ says the Doctor irritably. The henchman releases the remaining two aliens from their section of the lab. The Doctor asks Reegan how he is going to test the device if the aliens are let out, but Reegan ignores him, watching the aliens emerge into the main part of the lab. ‘They’ll be back,’ he tells the Doctor eventually. ‘What, more killing?’ asks the Doctor angrily. ‘Only if we have to,’ Reegan replies. ‘Get on with it, I want that machine finished by the time I get back.’ Reegan leaves and the Doctor sits back down to work. ‘You’re not just going to do as he tells you?’ Liz asks. ‘Come on Liz, let’s get on with it,’ says the Doctor. ‘We haven’t got much time, you know.’

Reegan drives the ‘Silcock Bakeries’ van up to the large metal front gates of an isotope factory, dons the headgear of his radiation suit, and releases the two aliens from the van. The aliens approach the gates; a security guard approaches the gates from the other side. Reegan sends a message using his one-way signalling device, and one of the aliens grasps a bar of the gates, instantly killing the guard on the other side. Terrified, the other security guard runs inside to the telephone. A touch from an alien’s left index finger destroys the lock on the gates, and the aliens open them for Reegan to drive the van in, as an alarm siren sounds.

At the Space Centre, Carrington has the third alien imprisoned inside two large concentric translucent cylinders. ‘We’ll be ready for your live telecast very soon, General,’ says reporter John Wakefield. ‘Splendid,’ Carrington replies. ‘Are you sure your men will be able to remove the helmet?’ asks Wakefield. ‘Quite sure,’ says Carrington. Wakefield is concerned that if there is indeed ‘some sort of alien creature’ inside the space suit, world panic could result.

Reegan’s theft of radioactive isotope is in progress. A police car races to the scene with its siren blaring. Reegan drives a low transporter vehicle with the crate of isotope on the back; then he and his colleague start to transfer the crate to the bakery van. The police car arrives and is met by the two space-suited aliens. Reegan uses the signalling device again, and the two policemen are floored by the creatures’ touch. The aliens get into the bakery van. One of the policemen, not killed by contact with the aliens, must get out of the way hurriedly as Reegan drives the van away.

The Brigadier tells Carrington the news that the aliens have raided an isotope factory, causing several deaths. ‘You see,’ says Carrington. ‘They’ve already landed. These creatures need radiation to live, and they’re prepared to rob and murder to get it.’ The Brigadier points out that there were men helping the aliens. ‘Traitors,’ says Carrington. ‘Collaborators, like your friend, the Doctor.’ ‘That is an unjustified assumption, sir,’ insists the Brigadier. Wakefield wants to know exactly what the General intends to say in his worldwide telecast. ‘I shall call on the nations of the world to unite in an attack on the aliens and their spacecraft,’ says Carrington. ‘It must be obliterated!’

The two aliens that were used to raid the isotope factory are back at the laboratory, where the Doctor and Liz are completing work on the communication device. Liz switches on the power, ostensibly to test the device. The Doctor tells Liz he has boosted the signal as much as he possibly can. He tells her to watch the aliens for a reaction while he attempts to signal to them, then begins to tap away at the machine. But the Doctor’s words are only for the benefit of the guard watching over them - he is actually signalling a Morse code message to UNIT.

At UNIT HQ, Sergeant Benton receives the message: ‘SOS’. He is surprised, because this signal has not been used for years. ‘Everybody’s picking it up, Sarge,’ says the UNIT radio operator. ‘Taxis, police cars, fire engines. It’s on a high impulse blanket frequency.’ Benton tells him to try to get a triangulation on the signal. ‘Save Our Souls,’ Benton muses.

Wakefield is practising for the telecast: ‘This is John Wakefield, talking to you live from the heart of Britain’s Space Control headquarters. This telecast is being received in homes all over the world by communication satellite relay.’ He breaks off to give instructions to his camera crew. Cornish asks Wakefield if he really thinks he should go ahead with the broadcast - General Carrington is going to call on the nations of the world to blast the UFO out of the sky with missiles.

At the laboratory, the Doctor tells Reegan that they are just about to test the communication device. Liz stays at the controls of the device while the Doctor goes up to the transparent screen behind which the two space-suited aliens can be seen. He speaks into a microphone: ‘Now we are trying to convert our speech into your radio impulses. Can you understand me?’ There is no response from the aliens, so the Doctor repeats his message: ‘We are trying to convert our human speech into your radio impulses, can you understand me?’ Still no response. ‘It doesn’t work,’ says Reegan menacingly. ‘Can you understand me, please try to answer,’ says the Doctor into the microphone. Finally, the two aliens turn towards the transparent screen and move slowly towards it, facing out into the main part of the laboratory. An alien voice, like the one the Doctor heard aboard the alien craft, is heard in the lab: ‘Why are we kept prisoners? Why do you make us kill?’ Reegan grabs the microphone from the Doctor and tells the creatures that if they do not obey his orders, they will be allowed to die. ‘We are ambassadors and came in peace,’ protests one of the aliens. ‘If you want to live, you’ll do exactly what you’re told,’ says Reegan. He congratulates the Doctor on the success of the device: ‘Now I can make a few plans.’ But he tells the Doctor to leave the device alone.

The alien ship transmits a message to the Space Centre; an image of the alien captain appears on the huge screen, watched by the Brigadier and Cornish. ‘Only a little time remains to you,’ the creature warns. ‘We have powers to destroy your planet totally, which we shall use if our ambassadors are not returned.’ ‘Now we know where we stand, gentlemen!’ declares Carrington. ‘We must attack first.’

At the laboratory, Liz and the Doctor stare grimly back at the thug holding them at gunpoint.

Carrington wants to make his television broadcast at once. Wakefield tells him that the worldwide hook-up will not be ready for another hour, but the General tells Wakefield he must speed it up - ‘this is an emergency’. A worried Cornish asks Wakefield what he is going to do, and the reporter replies that he is going to do as the General asks. The Brigadier is informed by telephone that UNIT HQ is picking up SOS radio signals, which he suspects may be from the Doctor. He tells Carrington that he would like to follow this up, but the General, seeming to grow more paranoid by the moment, calls him back: ‘You think I don’t know what’s been going on, don’t you?…that Doctor of yours is in league with these creatures. And you’ve been helping him!’ Carrington calls two security guards, and has the Brigadier placed under close arrest. Under protest, the Brigadier hands over his revolver to one of the guards. ‘I’ve suspected you for some time,’ Carrington tells the Brigadier. ‘All your UNIT people have been locked up, and replaced by men I can trust.’ The Brigadier is marched away. Cornish is about the telephone the ministry, but Carrington tells him it is too late: ‘All communications are under my control.’ ‘This Space Centre is under my control,’ Cornish retorts. ‘Not any longer,’ Carrington tells him.

In a shadowy tunnel leading out of the Space Centre complex, the Brigadier is marched along by the two security guards. Suddenly he overpowers them and hurries to a staff car, then drives away as one of the felled guards shoots after him. His car is allowed through the perimeter gateway just before the call arrives to alert the exit guards of his escape.

The UNIT radio operator tells Sergeant Benton that Space HQ have cut themselves off; Benton tells him to keep trying. The Brigadier arrives, and Benton reports that the SOS signals have cut out suddenly, but that they have managed to pin down the location of their source to a disused firing range quite near the Space Centre. There are only one or two available men at UNIT HQ, as most of the men are on duty at the Centre. The Brigadier says he will take what men there are. He tells Benton to keep the radio manned, and to get him a revolver and lay on a jeep. But all the transport is over at the Space Centre, and the engine of the staff car that the Brigadier ‘borrowed’ is too badly damaged by bullets. Benton suggests using the Doctor’s car…

…and with no other option, Bessie is soon racing through the woodlands with the Brigadier at the wheel and a handful of UNIT troops in the passenger seats. They stop, and the Brigadier spies Reegan’s ‘Silcock Bakeries’ van through his binoculars. They set off again, and pull up outside the laboratory building in time to engage in a fierce gun battle with two of Reegan’s heavies, who shoot from behind the cover of the van. This time there are no casualties. When Reegan’s men run out of bullets, the Brigadier orders his men to apprehend them. The two thugs emerge from behind the van with their hands up, but the two UNIT soldiers who move forward to arrest them are careless, and allow themselves to be overpowered. Now one of the thugs has a UNIT rifle. The Brigadier hurries forward and grabs him. They exchange blows, but the Brigadier ends the fight by knocking the man down a hill. The other man is easily apprehended.

Inside the laboratory, Reegan is examining a plan of a vault, and telling the Doctor about his scheme for using the aliens to blast it open. ‘Look, how many times must I tell you?’ asks the Doctor. ‘I am not joining you in a programme of bank robbery.’ ‘I’m offering you an equal share, Doctor,’ Reegan points out. Gunshots are heard, and Reegan sends his man up the laboratory steps to investigate. The Brigadier bursts through the door at the top of the steps and guns the man down. Reegan pulls out his own gun, but the Brigadier shoots it out of his hand. ‘Make yourselves at home,’ says Reegan suavely. ‘What kept you?’ asks the Doctor. ‘I see you’re all right, Doctor,’ says the Brigadier. ‘Miss Shaw?’ ‘Just get me out of here,’ says Liz. The Brigadier tells the Doctor that Carrington has taken over the Space Centre, and plans to make a telecast urging the world to attack the alien spaceship. The Doctor wants to stop him immediately, but the Brigadier points out that it will not be easy now that Carrington has arrested all the UNIT men and replaced them with his own troops. ‘We’ve got to get in there somehow,’ says the Doctor. ‘Why don’t you use them?’ asks Reegan, nodding towards the two space-suited aliens. ‘You know, I think he’s right,’ says the Doctor. ‘You won’t forget I thought of it?’ asks Reegan, looking after Number One to the very end. The Brigadier orders him arrested. The Doctor uses the communication device to say to the two aliens: ‘Now we’re going to return you to your own people. But first we need your help to prevent a catastrophe.’

Bessie and the ‘Silcock Bakeries’ van arrive outside the main gateway leading into the Space Centre complex. The Brigadier gets out of Bessie and, using a megaphone, orders Carrington’s men to open the gates. They ignore him; he repeats the order; they continue to ignore him. So now the two aliens are released from the van. The Doctor uses the communication device to instruct the aliens to open the gates. ‘Please try not to harm anyone,’ he adds. Carrington’s men begin firing on the advancing space-suited figures. The Doctor, Liz and the Brigadier take cover. The Doctor uses the megaphone to tell Carrington’s men that the aliens are invulnerable to their bullets; ‘they will not harm you, but you will die if you touch them,’ he warns. Carrington’s men, still firing, get out of the way as one of the creatures raises the barrier and both advance towards the complex. The Doctor’s party gets into Bessie. Each of the aliens touches half of the locking mechanism on the huge double doors leading into the complex, and the mechanism is destroyed. The doors swing inwards, and Bessie and the van are able to pass through.

Inside the Space Centre, Carrington is planning his television broadcast with Wakefield’s team: ‘When I move across to here,’ he says, ‘get your camera in close on this creature, and my man will forcibly remove his helmet. I want the world to know what these monsters look like.’ Wakefield agrees. Cornish urges Carrington not to make the broadcast, as it risks bringing down total destruction on Earth. ‘You have no concept of moral duty!’ declares the General. When Cornish continues to protest, Carrington has his security men remove him. ‘Five seconds to go, General,’ says Wakefield. Grimly dignified, Carrington gets ready.

Wakefield begins the broadcast: ‘This is John Wakefield, speaking to you live from the heart of Britain’s Space Control headquarters. This telecast is being received in homes all over the world by communication satellite relay.’ (Gunshots begin sounding in the background.) ‘Owing to widespread rumours concerning an unidentified flying object hovering above this planet, General Carrington, head of Space Security - himself an ex-astronaut and Mars Probe veteran - is about to speak to you on a matter of tremendous importance.’

A female technician screams as the two aliens enter the control room. ‘They’re here, we’re being invaded!’ cries Carrington, and starts firing at the creatures. The aliens stop their advance. UNIT troops, led by the Brigadier and accompanied by the Doctor and Liz, occupy the control room. The Brigadier holds Carrington at gunpoint: ‘It’s no good, General. I’ve released my men, this place is in my hands.’ ‘I must make this broadcast,’ Carrington protests. ‘It’s a matter of world survival!’ But the Brigadier replies that he must place the General under arrest. All the fight seems suddenly to go out of Carrington. He surrenders his gun to the Brigadier. But he carefully puts on his cap and takes up his swagger stick, determined to exit like an officer. Before he is taken away by Benton, Carrington pauses to say to the Doctor: ‘I had to do what I did. It was my moral duty. You do understand, don’t you?’ ‘Yes General,’ says the Doctor with great gentleness. ‘I understand.’