The Doctor joins Peri as she digs in the dust of an alien desert. He's surprised she hasn't collected enough samples already, but she couldn't resist when she saw this one -- it has a completely different leaf formation from the one she found on the other dune. She begins to explain her theories in great detail, then stops when she realises she sounds like she's lecturing him. The Doctor assures her that he's not bored and that he appreciates listening to people who have a passion for their subject. He adds that to the untrained eye, the landscape appears to be nothing more than an expanse of dead scrubland, but when Peri corrects him and says the proper term would be 'shrub land', he deliberately makes a point of emphasising the full extent of his knowledge of botany. She gets the point and asks him to carry her samples so she can take a look over a nearby rise.

As they move off, Peri asks if he had any luck following the footprints he spotted earlier, but unfortunately the wind had wiped the trail out once he got beyond the shelter of the dune. However, he did find a spanner, which must have been dropped recently as it wasn't corroded. Just as the Doctor concludes that there's humanoid life here somewhere, they hear voices coming from far away. They head towards a huge metal pylon in the distance and see two mechanics working on it. The Doctor wants to return their spanner, but as he heads towards them carrying Peri's samples, he thinks about being treated like a wheelbarrow. Peri laughs at his 'comment' and he realises that she read his thoughts. He theorises that the TARDIS's telepathic circuits might be out of sync, although he has no idea what could have caused it.

High up in the air, Sergeant Shreeni complains that the designer of the pylon didn't think to put the circuit hatches at the bottom instead of the top. His colleague Weiss calls out to make sure he's all right, but he's busy as he has orders from Major Taylor to make sure the net is boosted before the first colony shuttle arrives. Shreeni keeps getting electric shocks and asks Weiss to get the wave amplifier into position, but she tells him it's just residual power. His work is finished and she's just about to lock down her end of the cable when the Doctor and Peri arrive. As they introduce themselves, they hear a howl coming from close by. A Farakosh has got their scent, so Shreeni orders Weiss and the new arrivals to join him on the top of the pylon while he contacts the main outpost and asks for immediate Exotron support. There's no time for the Doctor and Peri to don the harnesses as a giant hyena-like beast appears and approaches them. The creature deliberately hurls itself at the pylon and the cable breaks loose, destabilising the entire pylon. The Doctor calls for Shreeni to come down from the top, but before he can do so, the entire structure is brought crashing to the ground...

As the dust settles, Peri and the Doctor crawl out from beneath the collapsed structure. They both seem to be unharmed, although their lungs are full of sand. They hear coughing coming from within the buckled metal, which tells them Shreeni is still alive, but they need to pull him to safety before the stunned Farakosh fully regains its senses. Once they know he's safe, the Doctor intends to help the creature too. Suddenly, a gigantic robot appears and strides towards them. The Doctor asks it to help the trapped man, but the robot ignores his request and instead opens fire on the defenceless Farakosh, killing it instantly. The Doctor is furious and turns to confront the new arrival.

In a darkened laboratory, the voice of Major Taylor speaks to the Exotron robot and orders it to make sure the Farakosh is dead, then help Shreeni and Weiss get out from the smashed pylon. Before it can do so, the Doctor's face appears on a scanner, speaking directly to the robot and demanding to know why it killed a defenceless creature in cold blood. Taylor is concerned to see there's a civilian in the area and he orders the Exotron to seize him and bring him back to the central net block.

The giant robot bends down and picks up the Doctor. He insists on being released and points towards the injured man who needs urgent medical attention, but the robot ignores his protests and carries him off into the distance. Left behind, Peri crosses over to Shreeni and is relieved to see that he's still conscious. She starts looking for a way to release him from the wreckage when another woman's voice calls out to her. Peri is delighted, but the new arrival addresses her sternly and tells her that if she lays one finger on Shreeni then they're both dead!

The Doctor introduces himself and pleads with the Exotron to slow down, but it does not respond. He guesses that the robot isn't sophisticated enough to think for itself, so it's probably being controlled by a remote device. He spots a speech grille on the robot, yet the metal giant appears to have no inclination to communicate. He also deduces that the robot was designed by the military as it has their customary un-aesthetic style, but it can't be programmed with the normal field training protocols or else it would have stayed to help Shreeni. Back at the main compound, Major Hector Taylor is observing events and wonders where the stranger has come from. At first he suspects the Doctor might be working for Ballentyne and has come to check up on him, but it soon becomes apparent that the stranger doesn't know anything about the Exotron Project. When the Doctor theorises that someone may have overridden the military protocols, Major Taylor concludes that he must have been sent by Earth Authority to take the Project from him! He orders the Exotron to bring the Doctor back quickly...

The woman who warned Peri away from Shreeni tells her the power from the pylon is still live. She switches it off and points out that if Peri had touched him, she'd have earthed the circuit and fried them both. The woman checks on Shreeni's condition, then regretfully tells the Sergeant that Weiss is dead. Peri helps the woman clear the debris, and tells her they were attacked by a big mutant hyena. The woman is surprised that Peri's never heard of the Farakosh before, then realises she must be from off-world. She assumes Peri must have come from the colonists' shuttle, although it isn't due to arrive until later that afternoon. Peri tactfully changes the subject and they get back to helping Shreeni. The woman explains that the Farakosh were top of the food chain until humans arrived to terraform the planet, but they usually don't attack unless they're provoked. They pull Shreeni clear and the woman says he should be OK once they get him back to base, and then she'll have a few choice words to give to Major Taylor, the commander of their outpost. The woman introduces herself as Paula Taylor, head of the geological team, chief terraformer -- and the Major's ex-wife! They start heading back to the base and Peri realises they're going in the same direction in which the robot took the Doctor.

The colony shuttle is due to arrive in 95 minutes, so the compound personnel prepare to take up their welcoming positions. The Exotron robot carrying the Doctor arrives and lowers him down in front of an armed reception committee. The lead soldier, Corporal Mozz, tells him he's going to meet the man in charge, Major Taylor. The hangar doors are opened so that the Exotron can go inside to power down while the Doctor follows Mozz further into the compound.

Inside his office, Major Taylor is completely exhausted, but he's unable to get the rest he needs as Corporal Mozz arrives with an “unidentified male”. The Corporal is asked to wait outside and then Taylor asks the Doctor to explain how he was able to land on the planet without being detected by the sensors. When Taylor addresses him by name, the Doctor realises there must have been a monitoring device inside the Exotron that brought him here. Taylor is impressed by the Doctor's ingenious reasoning and asks him how much he knows about the Exotrons. The Doctor avoids the question, but assures him he has nothing to hide -- although he's not sure he can say the same about Taylor. The Major becomes angry and accuses the Doctor of being sent by Earth Authority, but the Doctor returns the anger and demands an explanation for the brutal killing of a creature at the hands of Taylor's organisation. Taylor tells him the Exotrons defend them against attack from the Farakosh, but the Doctor points out the animal was utterly defenceless. Taylor insists that he was only able to bring this outpost in under budget and on time by creating the Exotrons. The Doctor suspects this was done without the Authority's knowledge and wonders what Taylor is hiding.

Taylor is convinced the Doctor has been briefed by Ballentyne, Secretary for the Interior, and is here to take the Project away from him. The Doctor asks him if there's something about the Exotrons that he's ashamed of, because whatever it is, it's stopping him from sleeping. The Major's skin is grey, his eyes are hollow and his body is gaunt -- his obvious exhaustion, coupled with the fact that he monitored the Doctor's arrival through the Exotron, suggests he is somehow controlling the robots, possibly through a form of cerebral link. The interface would need to be close by and the Doctor indicates a door at the back of the office. Taylor demands to see his Earth Authority identification, and when none is forthcoming, Taylor calls Corporal Mozz back in. He accuses the Doctor of being a spy, here to undermine their terraforming policy. He orders Mozz to escort the Doctor to the interrogation block, and as he is dragged away, the Doctor warns Taylor that the implications of creating a telepathic network that controls robots over great distances are unfathomable. Even if he disregards the cost to his own health, Taylor should think of the devastation that could be caused by a robotic army controlled by a single military mind. The Major reminds him the Exotrons exist to protect this settlement and he assures the Doctor he knows exactly what he's dealing with.

When Shreeni tells Paula that the Exotron saved their lives, she appears to be sceptical. She refers to the Exotrons as her ex-husband's “pet project” and says they were originally designed to protect her geological team whenever they had to work a long way from the outpost. Peri wonders why she doesn't have an escort with her right now, but Paula assures her the Farakosh never bother her when she's on her own. She says there's no reason to be scared of them and in the whole two years they've been there, the creatures have never done anything other than stare at her. In fact, they only seem to go crazy when the Exotrons are around. Peri remembers that the Farakosh seemed to be attacking the pylon rather than Shreeni or Weiss, so perhaps they don't like metal. Paula agrees, especially when she learns that the mechanics were boosting the Exotron net signal from the pylon. She thinks the Farakosh only attack people when the Exotrons turn up, but Shreeni doesn't agree and he's convinced the animals are planning something and will kill them all if they get the chance. They seem to have been getting worse recently, with more and more of them massing around the compound. Paula has studied the animals and is satisfied they're not hostile, but her ex-husband has always refused to listen to her. Peri asks about their relationship and Paula says they still try to be friends, but it's not been easy since the divorce. In the end, she had to threaten to stop conducting the geological surveys if he insisted that she take an Exotron with her, but he still refused, so now she has to sneak out to do the work on her own.

Major Taylor makes a call to Secretary Ballentyne and demands to know what's going on. He also complains about being re-routed from the usual number at Ballentyne's Brussels office to a personal line, but Ballentyne assures him he's simply being discreet in having calls from certain numbers diverted. Taylor tells him there's an Earth Authority agent here asking questions about the Exotron Project, but though he assumes the Doctor must have got information from Ballentyne, the Secretary says that's ridiculous. Even if they had cause to be suspicious, there's no way anyone could trace his private funds. He warns Taylor that there's a lot riding on this Project, not least of which is Taylor's reputation, but the Major believes things are getting out of hand. He says he only started it to protect his wife, but Ballentyne reminds him that if it hadn't been for his investment, Taylor would be up to his neck in debt. He tells Taylor to pull himself together and act more like a soldier. They agreed together to change the direction of the Project and the risks seem to have paid off. Selling it to the military is going to be the easy part. Taylor calms down and admits that he's tired and guiding the Exotron net hasn't been easy, but Ballentyne isn't interested in his sob story. Taylor assures him that when the first colony ship arrives, it will be protected by three full units of Exotrons. It wouldn't do for the first arrivals to step off their ship and straight into the jaws of the Farakosh. Ballentyne tells him to forget about the Doctor, but Taylor is beginning to suspect that he might even be an independent arms trader. When the call ends, Taylor is notified that his ex-wife is outside the base. He's furious that the soldiers have allowed her to give them the slip once again, so he orders a squad of Exotrons to go out and collect her.

Corporal Mozz escorts the Doctor to a lift that will take him down to the detention area. He ignores the Doctor's attempts to mock him, but thinks to himself that he only needs one excuse to put a bullet in his prisoner. Oddly, the Doctor is able to hear his thoughts, so he sends back a thought to the Corporal reiterating what the soldier said. For a moment, Mozz is confused and the distraction is just enough for the Doctor to push him into the lift. He presses the button for the basement floor and watches as the doors close, with the soldier trapped inside. Mozz tries thumping the lift controls, then opens fire on them, causing the lift to break down. He forces open the doors and starts shooting at the fleeing Doctor. He uses the intercom to send out a base-wide alert for the Doctor, who disappears down a stairwell. He orders the other soldiers to shoot to wound rather than kill, but then he thinks to himself that the Doctor had better pray the others get to him before he does...

With alarm bells ringing all around him, the Doctor pauses for a second to get his bearings. He finds an empty office and hides, just out of view. He sees Corporal Mozz outside the door searching for him and hopes that he doesn't think to look inside. Unfortunately, Mozz heads straight for the Doctor and warns him not to try any more of his mind tricks. The Doctor realises the soldier was able to hear his thoughts. He tries to explain that this outpost, and the area around it, seems to be saturated with telepathic fields -- and to prove his point, he deliberately speaks to Mozz inside his head. The soldier tries to resist, but the Doctor wants to test another theory. Some scholars say that when two minds are connected together, they don't just converse, they can also influence each other. In an area awash with liberal quantities of telepathic energy, a strong mind already versed in the rudiments of telepathy can influence the other. Slowly, the Doctor instructs Mozz to lay his gun on the table, then go back to his quarters to lie down. Convinced that he wasn't able to find his prisoner, Mozz turns and leaves the office. Alone once again, the Doctor starts to realise that telepathy might be the key to everything that's going around here.

Paula orders the Exotrons to cease firing on the Farakosh, but to no avail. Then, one of the giant robots comes over to her and physically lifts her into the air. She begs the machine to go away, but they're joined by another two robots who pick up Peri and Shreeni too. Hanging on for their dear lives, the group prepare themselves for a bumpy ride back to the compound. Before long, they see the outpost appear on the horizon, but the Farakosh appear to be moving in the same direction! The creatures head for the main entrance, as if planning to storm the place.

In the darkened laboratory, Hector Taylor is watching events unfold through the eyes of the Exotrons. He doesn't recognise Peri and concludes that she must be another spy. Things are getting out of hand and now the Farakosh are attacking like never before! The other Exotrons try to lead the Farakosh away from the compound while the robots carrying Paula, Peri and Shreeni turn away and head off for yet another destination. Major Taylor is confused by the robots' actions, as he didn't order it. He demands they bring his ex-wife back to the main compound where she'll be safe and is frustrated that they don't seem to be listening to him.

The Doctor is pleased to discover the compound uses old-fashioned computers as they're easier for him to break into. He finds the frequency specifications for the Exotron net and lays down on the floor to read them. If the TARDIS isn't too far out of range, he should be able to link with its telepathic circuits and use their power to force his way inside Taylor's science project. He mentally opens up the doors to perception, but as soon as he does, he's overwhelmed by many voices calling for him to help them. Eventually the voices start to settle down, until the Doctor can hear just one above the others. The voice says they've been waiting for him and it pleads with the Doctor to help them -- but then the voice of Major Taylor breaks in and tells the Doctor he's not welcome here. The Doctor snaps back to reality with a start, now certain there's some kind of constructed telepathic link at work here.

The three Exotrons carry Paula, Peri and Shreeni to safety, but surprisingly they drop them off at the geology block rather than the main compound. Peri assumes they must have recognised where Paula works, but Paula says they're just unthinking tools with no capacity for intelligence. Despite that, Peri has noticed that the Exotron who carried Paula doesn't seem to want to leave her alone. If she didn't know any better, she'd think it was fond of her. She wonders if Hector specially programmed this one to look after her, and Paula thinks it would be typical if her ex-husband was trying to be nice and ended up doing the one thing that would annoy her the most. She decides their priority should be to get medical care for Shreeni, so they go inside.

Apart from a few broken ribs, Shreeni's injuries are mainly cuts and bruises, so Paula's confident he should be back at work in no time. She gives him an injection, then tells him to get some rest. Peri wants to find the Doctor, which reminds Paula that she doesn't really know much about them. She assumes they came from the colony shuttle, but she's sure she never heard it land. Peri tells her they're just travellers who landed here by mistake, and Paula can see from her appearance and demeanour that she hasn't come from Earth Authority. Paula suspects Hector has been using the outpost as an excuse to develop the Exotrons beyond what was originally intended. He may claim he's been doing it to protect them from the Farakosh, but Paula is absolutely convinced the creatures are no danger anyway. Peri wonders if Taylor might be conducting top secret tests on the robots for the army, but Paula thinks it might be worse than that. The outpost doesn't get much funding from Earth, and the less money they ask for, the greater the bonus given to everyone when the first colonists arrive. This means Hector is getting his money from somewhere else, perhaps even from a private source, which means he must be planning to sell the whole Project to the highest bidder for maximum profit. This makes him no better than an intergalactic arms developer. Paula can't believe her ex-husband has changed so much, but Peri reminds her this is all speculation and they don't know how much of this is true. Maybe Hector is just trying to make up for past mistakes? Paula points out that he has nothing to make up for -- it was she who had the affair and cheated on him. Hector was always the good guy!

A frustrated Taylor orders the Exotron accompanying Paula to regroup with the rest of its unit, but it refuses to leave the geology block. First it disobeyed his order to bring Paula to the main compound and now it won't leave her side. Suddenly he realises who the Exotron is, and he knows what it's doing!

Paula tells Peri more about the affair she had when she was still married to Hector. Her lover's name was Christian and he was a lieutenant, but he was killed six months ago by a Farakosh. Peri is confused as Paula has always insisted the animals are harmless and wouldn't attack people, but she explains that it was Christian's own fault and he was acting like a typical soldier. In any case, Paula doesn't regard the Farakosh as animals in the pejorative sense. She thinks they have reasoning minds and she swears that she's seen them actually listening to each other sometimes, even though they don't make any sound. Paula's team have been taking sonic readings to measure the strata and clarify its composition. The military don't regard it as a serious part of the terraforming project, but it is part of the colonisation regulations. Peri is intrigued to discover they're using sonics and wonders if that's what the Farakosh are listening to? Paula agrees and concludes that the Farakosh must think they're setting up the rigs in order to communicate with them, which would also explain why they never attack her. She starts to collect together another sounding rig and prepares to go back outside, but Peri warns her there are probably hundreds of Farakosh out there now. Paula has never seen so many at one time, but if she can successfully get through to them, she can persuade them to leave and save them from being slaughtered. Just then, a base-wide announcement is made calling all personnel back to the central net block as the Farakosh have breached the perimeter defences. Peri wants to join the others in the main compound, but Paula warns her she'll never make it with all the bullets flying around. Paula asks Shreeni to help Peri use the monitors instead as they're linked all over the outpost, then leaves, carrying the sounding rig.

The Doctor is still trying to find a way into the telepathic link when he hears Peri's voice calling for him. He turns to a nearby monitor and sees her with Sergeant Shreeni in the geology block. She wonders what the Doctor was doing on the floor and he explains that he was trying a simple telepathic trance. He tells her the whole area is flooded with telepathic activity, which is how the Exotrons communicate. Peri says Paula has gone outside to test her theory about the way the Farakosh communicate, but the Doctor has no idea who Paula is. Peri fills him in and the Doctor decides it's time he had another encounter with Major Taylor. Peri warns him the Farakosh have broken into the compound, and with all the Exotrons and soldiers heading back there too, he'll soon be in the middle of a war. He asks if she has access to all the security cameras, and when Shreeni confirms they do, the Doctor starts building a portable communicator so they can use the cameras to guide him along the safest route back to Major Taylor's office.

Paula makes her way out into the desert, still accompanied by the ever-loyal Exotron. The air is filled with the sound of gunfire from the robots and howling from the Farakosh. Deciding her companion might as well make itself useful, she orders the Exotron to set up the sounding rig in a nearby clearing. She's unaware that their every movement is being watched by an increasingly bitter Major Taylor. He knows the Exotron is trying to impress Paula and he thinks it's pathetic. Could his ex-wife bear to stand next to the robot if she knew who it really was? Taylor believes he should be the one to protect Paula, not the robot.

The Doctor moves out into the corridor and asks for directions from Peri. His makeshift communicator is working and she quickly picks him up on the internal camera system. She starts to lead him off, but as he turns the corner he sees a huge Farakosh being cut down by rapid gunfire from an Exotron. He's outraged by the mass slaughter that's going on, but Peri calls him back and tells him to run in a different direction. Eventually he comes to a stop near a junction, but when Peri checks the scanner the fighting seems to be everywhere. Fortunately it doesn't seem to be coming any closer, but she can't find a safe route for him, so Sergeant Shreeni steps in and together they check the output from all the nearby cameras. Peri is alarmed when she picks up Paula on another monitor and sees the Farakosh heading straight towards her from every direction. She wants to go out and warn her, but the Doctor tells her it would be too dangerous. He's intrigued when she points out it's the Exotrons that are making the Farakosh angry, but unfortunately Paula has one with her right now. The Doctor thinks he recognises the area he's in now, so he should be able to make his own way. They wish each other luck and head off on their separate missions. Shreeni has no wish to let Peri go out on her own, so he decides to accompany her.

Paula passes a connection to the Exotron and is just about to activate the sounding rig when she's distracted by a sound from above. To her amazement, the colonists' shuttle flies overhead and comes in to land within the compound area. Also outside the compound, Peri and Shreeni see the Earth shuttle coming in to land too. They hear the growling of nearby Farakosh and Peri worries they may already be too late to save Paula.

The Doctor reaches Major Taylor's office and heads straight for the door leading to the inner sanctum. He finds a security coder, and without pausing, he types in the correct five-digit number. The door slides open and he's greeted by the sight of the frail Major connected up to a cerebral link interface. Taylor demands to know how he found the door code, but the Doctor tells him he was able to read his mind. The Doctor wants the Major to unplug himself as he can tell immediately that the intravenous implants must be causing him great pain. Taylor fights for breath and tells the Doctor he can't unhook himself -- if he loses concentration, the entire outpost will be overrun by the Farakosh. It's his will alone that controls the Exotrons, yet the Doctor has noticed another robot in the corner which appears to be completely inert. Taylor warns the Doctor away, but he realises he's close to discovering the whole secret. Ignoring the Major, the Doctor takes a close look and is horrified by what he finds -- the outer casing of the Exotron is connected to the body of Weiss, the soldier who was electrocuted by the pylon earlier today. Taylor confirms that to all intents and purposes, Weiss is dead, but an Exotron got to her soon enough to revive her brain activity. Then he had her body brought here and she's being kept alive by a life-support system in preparation for something...

The Doctor accuses Taylor of being a grave-robber, and wonders if he's been trawling the medical block and falsifying death certificates. It's unlikely he asked for volunteers as the process looks painful. He reveals that he learned the door code to this room after breaking into the net, albeit for a brief moment, and seeing inside Taylor's mind. Now he knows what Taylor is up to -- the Exotrons are mere shells, they're not robots at all. Fused inside each case is the fatally wounded body of a soldier, kept alive in mortal agony. Taylor warns the Doctor that if he tries to pull him bodily from the interface, he'll kill him. The Doctor considers whether there's another way to get inside the net. He grabs hold of Weiss's Exotron suit and tries it on for size. Taylor warns him that the process is irreversible and once he connects himself to the suit, he'll be enslaved for life! The Doctor believes he has no choice if he's to save the two species on this planet from mutual destruction. Taylor quickly orders all Exotrons to return immediately to the central laboratory, but it's too late. The Doctor overrides Taylor's neural link and then climbs inside the metal shell of the Exotron.

The Earth shuttle completes its landing within the compound and the soldiers aboard prepare to disembark. With them is Secretary Ballentyne, who appears to be looking forward to the fun ahead...

The Doctor is once again overwhelmed by voices inside his head and he finally understands just how many enslaved lives are contained within the net. He tells the voices that he's here to help and slowly the babble becomes one single voice, speaking on behalf of them all. The Farakosh are inside the net with them too. The voice explains that the creatures are natural telepaths and the Exotrons enrage them because the white noise of the net sears across their senses. Peri was right all along -- the Farakosh only fight because whenever the Exotrons are activated, it causes them pain. The Doctor calls out to Taylor and demands to know whether he knew about this, but the voice points out that Taylor can't hear them. Only the other minds in the net can hear him -- and they've been waiting for him...

Peri and Shreeni race over to Paula to see if she's all right. They tell her there are about half a dozen Farakosh heading this way, so they need to get out of here quickly. Paula is almost ready with the sounding rig, but with the Exotron here too, the Farakosh will be provoked into attacking. Paula orders the robot to return to the hangar, but it refuses to move. Shreeni suggests they try heading for the shuttle instead, but Paula is determined to find out whether the Farakosh are really trying to communicate with them, and the sounding rig is the only way they can get them to stop the carnage. Peri reminds her this is all just guesswork and she may be wrong, but it's too late now anyway as one of the Farakosh arrives and approaches them...

The voice tells the Doctor that the living hell he's now experiencing is a single consciousness where everything, including sight, knowledge and pain, is shared. It's a telepathic gestalt, and now the Doctor can feel the communal awareness too. He even recognises the voice as that of Lieutenant Liptoye, a man he's never met before. Liptoye knows the Doctor has a unique, extraordinary mind, but he warns that it will only take a few moments for the net to imprison it permanently, so he plans to push the Doctor's mind out before the assimilation is complete. The Doctor protests as he's confident he can take control of the net from Taylor, but Liptoye tells him he doesn't need to do that. The fact that a mind as individual as his has entered the gestalt has been enough to disturb the harmonics and give the others the strength they needed. Liptoye has been fighting against Taylor's orders for a long time and he gains a little ground with each attempt, and when he learned the reasons why the Farakosh were attacking them, he was able to resist the orders to kill them. Now, thanks to the Doctor, he can feel himself becoming completely independent. He will soon be strong enough to openly challenge Taylor for control. The Doctor realises he can see Peri through the eyes of one of the Exotrons and Liptoye explains that this is the shell that contains his rotting body. He's been looking after Paula all this time, but the Doctor can sense that it's more than just protection. He can feel the love that Liptoye has for Paula and realises he was her lover, Christian! Paula thinks he's dead and that's the way Christian wants it to stay. He warns that the net is starting to assimilate the Doctor's mind, so he thanks him and then forcibly ejects the Doctor's mind from the gestalt.

In the real world, the Doctor bursts out of the Exotron shell and stumbles over to an increasingly frail Major Taylor. The officer is mumbling about the pain and loss he's experienced and insists that he had no idea. The Doctor pleads with him to stop the project.

Elsewhere, Alpha and Omega squads are preparing to disembark from the Earth shuttle that's just landed. Secretary Ballentyne orders Alpha squad to proceed immediately on foot to the central net block, while he will accompany Omega squad aboard the shuttle which will take off again and land on the roof of the compound itself. Before they leave, he gives orders for the troops to kill anything that moves...

In the desert, Shreeni notices that the fighting has also stopped and the Exotrons are no longer attacking the Farakosh. Paula realises the sounding rig is starting to work and that the Farakosh before them is trying to communicate. A female voice echoes around them, but Paula is certain it didn't come from the Farakosh as she was watching it all the time. They soon realise the voice is coming from the Exotron, and the Farakosh explains that she's using the robot's devices, together with the human voices inside the net, to communicate with them. The creature introduces herself as Kucha. Paula apologises for what's happened, but Kucha says she understands. Shreeni is amazed the animals can talk, but Kucha explains that it's come about because Peri's friend the Doctor has allowed someone else to control part of Major Taylor's net. Paula wonders why Kucha isn't attacking the Exotron and she explains that the net disrupts their natural telepathic field, but the vibrations in the sounding rig are harmonising that disruption so that it stops the pain. As long as the sonic device is working, the Farakosh can live in peace with the humans. Peri interrupts and points out that the group of people currently disembarking from the shuttle don't look much like civilians. Before anyone can react, the soldiers immediately start shooting at everything in the area. The Exotron stands in front of Paula, but she orders it to protect the sounding rig instead. She tells Kucha to get away quickly, but before Kucha can react, she is shot. As she cries out in pain, Shreeni calls on the advancing soldiers to cease fire and warns that there are civilians present -- but then he too is hit with multiple bullets. His body falls to the ground and although Paula does all she can to revive him, it's too late. When the sounding rig itself is destroyed, Peri calls out to the injured Farakosh and urges her to keep the Exotron between her and the soldiers, then run to safety as soon as she can.

Major Taylor realises the Earth Authority troops are storming the compound. He does his best to hold them off using the Exotrons, but the Doctor can see that the effort is killing him. Taylor pleads with Christian to save Paula, but the Doctor urges him to close down the net, if only to save his own life. Taylor breaks down with a mixture of exhaustion and stress over what he's done. He's created a self-sustaining circle of violence and he knows that everything has been his fault. Just then, Secretary Ballentyne comes through on the communicator and informs Taylor he's come to collect on his investment. Things are getting out of control, but the Doctor tells Taylor he can still stop all this...

Aboard the shuttle, Ballentyne instructs the pilot to set them down on the roof. Suddenly they receive an emergency call from Alpha squad reporting that they're under attack and being wiped out -- but before the soldier can give any further information, there's a scream and the line goes dead.

Paula, Peri and the Exotron manage to get to safety, but unfortunately they didn't see what happened to Kucha. This is all so senseless and with the sounding rig destroyed, there's nothing they can do to calm the other Farakosh down. Paula is convinced Earth Authority has come to take the Exotron Project from her husband and they must have used the colonists' ship as cover. Peri wonders whether Taylor knew about the pain he was causing the Farakosh, but Paula is sure he didn't. He may be obsessive, but he's not cruel. Peri remembers Kucha talking about human voices in the net, but Paula doesn't know what she meant. She suggests they follow the soldiers back to the central net block and do whatever they can to find her husband. As she turns, she finds her way blocked by the Exotron and she lashes out at it angrily, calling it a freak.

The shuttle lands on top of the compound and the soldiers begin to disembark. They move swiftly and spread out across the roof, with a small squad following Ballentyne's lead as he heads for Taylor's office. They hear a commotion coming from a nearby stairwell and then reports start coming in from all over as the soldiers come under attack from the distressed Farakosh. Ballentyne orders his squad to cover him while he gets the door to the other stairwell open, but as soon as the Secretary enters, he slams the door behind him, locking the soldiers on the other side and leaving them to the mercy of the creatures.

Taylor doesn't have much strength left, but he forces himself to contact Christian over the telepathic net. He tells him to take control of the Exotrons and lead them to the roof to assist the Farakosh against the Earth Authority soldiers. Taylor thanks him for looking after Paula, then asks the Doctor for help in detaching himself from the equipment. Now that the net has been disconnected, the Exotrons will be shutting down all over the outpost, which will relieve the creatures of their pain.

Moments later, Peri, Paula and the Exotron arrive and join the Doctor and Taylor. The Doctor warns Paula to prepare herself for the worst and when she sees her ex-husband, she realises he's close to death. He tells her she was right about everything, but she tells him he made a mistake, nothing more. He doesn't think he was a good husband to her and she didn't deserve that. She assures him he was at the beginning, but that she wasn't a good wife, at least not at the end. They laugh together and in his dying breath, he tells her he's glad that she was here at the end. Peri comforts Paula, but just then Secretary Ballentyne arrives and covers them all with a weapon. He introduces himself as a former business partner of the late Major Taylor and blames Paula for leaving her husband, which resulted in him going to pieces. That put their project at risk, so he had to make plans to come here and “relieve” him of his responsibility. The Doctor moves to dismantle the net apparatus, but Ballentyne fires a shot to warn him off. He gets ready to download all the details of Taylor's research, which he then intends to sell to the military. He'd planned to kill Hector too, but of course that's no longer necessary. Paula threatens to destroy the entire outpost before she'll let him take the research, but Ballentyne was going to do that anyway and he's come prepared with the self-destruct codes.

Ballentyne steps forward to retrieve the research, but the Exotron orders him to stop. The Secretary is momentarily surprised as he thought all the robots had been shut down, but then the Exotron starts smashing the equipment around the room and within seconds, the hard drive of the computer is completely destroyed. Ballentyne says he will simply take the working Exotron back with him to be dismantled by his experts. He raises his weapon to remove the witnesses, but then the Exotron disarms him and clubs him to the floor. The Doctor thanks the Exotron -- but when it replies, Paula recognises his voice. The Exotron admits that there's no easy way to tell her the truth, and Paula is shocked to discover he is Christian. Peri asks if he's trapped inside the robot, but Ballentyne explains that the body is just rotting flesh, and all that exists of the man Paula loved is his neural network. In the momentary distraction, Ballentyne jumps to his feet and activates the self-destruct mechanism. An alarm sounds and they realise the whole compound is about to go sky high. Ballentyne makes his escape while the Doctor concentrates on undoing the damage, but unfortunately it's too late. The Exotron containing Christian reveals that he can now control the net and is summoning all the other robots here. Together, they might be able to smother the blast so the explosion will be localised just to the laboratory. The outpost itself will be saved and they'll have enough time to get any survivors clear. The Doctor points out that it was Major Taylor's manipulation of the net that caused so much pain, but now that the Exotrons have their independence, they can all live here in peace with the Farakosh. Christian knows the Farakosh would welcome them, but he believes it wouldn't be much of a life being mostly machine. There's no other way, and even when Paula pleads with him to reconsider, he insists on going ahead with the sacrifice. He's sorry about what happened to Hector and he's even more sorry to have to leave Paula again, but at least he's had another opportunity to tell her he loves her. He asks the Doctor to take the others to safety.

Some time later, the Doctor leads everyone who they managed to find in the compound to the safety of some distant dunes. Many of the people are wounded and Peri insists they stop for a rest. They should be far enough away now, so the Doctor agrees. Paula still believes they shouldn't have left the Exotrons behind, but the Doctor reminds her it was their own choice. He could see into Christian's mind and he knew there was no way they were going to change it. Paula is angry that Ballentyne got away, but the Doctor suspects it's the end of his career -- he won't be able to cover up something on this scale and he'll be hounded from office. Just then, Paula hears Christian calling her name telepathically. He tells her he's glad they got the chance to see each other again, then they bid each other farewell as the compound computer reads out the countdown to self-destruct...

In an expensive restaurant somewhere on Earth, three gourmets plan their evening. Commander Edge becomes frustrated and insists that they all agree once and for all that the Doctor must die! Captain Kettoo urges him to keep his voice down as they're supposed to be blending in with the humans. Co-ordinator Harom is more concerned about wasting away himself if the waitress doesn't get a move on with their appetisers. He begins to lecture his fellow diners about the origin of the goulash he's ordered, and Kettoo mocks Edge for having no appreciation for food. Wherever they go in the universe, he always orders the same thing -- steak and chips. Harom brings them back to the matter in hand. They all agree that the Doctor is guilty, but killing him would be outside Inquisitor Oron's brief. Edge argues that as members of the CIA, they have a duty to exceed their brief and points out that the Doctor's actions warrant the severest punishment. Kettoo agrees and says the atrocities carried out by the Doctor on the planet Poytee are almost unparalleled. Harom only wants a quiet life, so he goes along with their suggestion. All they have to do now is wait for the Doctor to arrive. Inquisitor Oron's interpretation of the Doctor's time signature indicates he should be putting in an appearance here sometime this evening, but it's impossible to be more precise than that.

Just then, the waitress arrives with their appetisers -- and the plotters have no idea that she is actually Peri. She apologises for the delay and says that the chef is in one of his fiddling moods and insists on adding extra ingredients. Edge is impatient with her and Kettoo has to apologise for his behaviour, claiming he's had a difficult day in the office where they all work, but her over-the-top attempts to appear normal only exasperate Harom. Peri laughs it off and says she's used to it. They get all sorts dining here and sometimes the customers are so weird it's like they're from a different planet. She leaves and Edge becomes suspicious, but Harom dismisses his concerns. Edge can't believe his colleagues have any appetite left after what the Doctor did on Poytee and he thinks they would benefit from being reminded. Or perhaps it's just that he remembers it differently to them? As he recalls, from the moment the Doctor arrived on the lawless blot on the galactic landscape, he took it upon himself to be judge, jury and executioner...

The TARDIS materialises on Poytee and a miserable Peri dismisses the planet straight away. It's every bit as bad as the Doctor said it would be -- the entire surface is a single, moral-less conurbation with people killing each other on the street. The Doctor says the planet has always had the reputation of being an insidious little hole, but at this point in its history, the people have reached the height of their cruelty to one another. The watch as a screaming inhabitant runs past and is cold-bloodedly shot down by another. The Doctor is indifferent to the man's suffering -- whoever he was, he probably deserved it.

Moments later, a vehicle comes screeching around the corner and heads straight towards them, its occupants firing weapons randomly in all directions. As it disappears into the distance, the Doctor helps Peri to her feet. He's furious and promises that the street rats responsible won't get away with it. He heads back into the TARDIS to open up the cache of weapons he keeps in the armoury under the console. The vehicle must be several blocks away already, but he's confident it won't be able to outrun one particular weapon, if only he can remember the priming sequence. With Peri holding the back of the weapon to keep it steady, the Doctor lifts it onto his shoulder and opens fire. A burst of energy shoots out and the Doctor and Peri cheer and leap for joy when it hits the intended target. The Doctor is delighted with the weapon and proposes taking a consignment back to the Brigadier. And now, it's time to sort this planet out. These people have to be taught a lesson and the Doctor's just the Time Lord to do it! He hands Peri another weapon and warns her to be careful where she points it, then they head for their next target -- in the penthouse on top of a nearby tower.

Planetary Co-ordinator Palgrave switches nervously between the various channels on his comms unit, but they all show the same thing -- death, destruction and suffering. Suddenly the door explodes and the Doctor and Peri stride in, cocking their weapons. Palgrave asks how they got past security, but Peri tells him he'd never believe what level 3 on their pistols can do to a humanoid body. The Doctor demands the terrified man confirm his identity and when he does, the Doctor shoots him dead at point-blank range. Peri laughs as the Doctor accesses Palgrave's computer and sets the global network of sub-surface atomic generators to overload. As the planet starts to shake from a series of explosions, the Doctor declares their work here is done. They should just have enough time to get back to the TARDIS before Poytee's upper mantle ruptures and the surface of the planet becomes awash with cleansing lava. As they leave, the Doctor's only remaining concern is how he's going to get the blood out of his shirt...

Kettoo is confused. She thought this was how the story went, but now that Edge has told it again, she's not so sure -- it just doesn't seem very characteristic of the Doctor. Harom asks Edge if he's sure he got all the details right? They know the Doctor is a subversive, but somehow this doesn't seem right. Edge agrees that it seems a bit extreme now he comes to think of it. Peri returns to the table and asks how they found their appetisers. They agree that the food was delicious, although they question its interesting after-taste, but Peri refuses to reveal any of the chef's secrets. She then hands out the main courses, including steak and chips for Edge. Harom returns them to the matter in hand. If they're agreed that Edge's version isn't how it happened, then what did? Kettoo thinks she knows where his story got a little exaggerated, and she now remembers what really happened after the Doctor and Peri arrived on Poytee. It's true that the planet was gripped by what seemed like a global riot, but she thinks the Doctor's cruelty was actually prompted by some sort of twisted desire to help...

The TARDIS materialises on Poytee and a miserable Peri notes that the planet is every bit as bad as the Doctor said it would be -- she feels sorry for the poor people that have to live like this! The Doctor says the entire surface of Poytee was terraformed as a single conurbation, which can produce some unique pressures, but he's never known it to be as bad as this, so something must have happened.

Moments later, a vehicle comes screeching around the corner and heads straight towards them, its occupants firing weapons randomly in all directions. As it disappears into the distance, the Doctor helps Peri to her feet. He's furious and promises that the street rats responsible won't get away with it. He produces a cricket ball from his pocket and delivers a googly that goes right through the windscreen, hits the driver and causes the vehicle to crash. The Doctor is determined to know what's going on here and he believes the best place to find out is in the penthouse on top of a nearby tower.

Palgrave switches nervously between the various channels on his comms unit, but they all show the same thing -- death, destruction and suffering. He's desperate to find a way to resolve their problems quickly and prevent more people from dying. A trooper arrives, escorting the Doctor and Peri, who introduce themselves warmly. The trooper orders them to be quiet and reports that they were captured on level 15. They asked to speak to Palgrave urgently and she agreed after the bio-scan confirmed they weren't infected. The Doctor and Peri realise this means the whole population has been infected with some kind of frenzy-inducing virus. Without waiting for permission, the Doctor accesses Palgrave's computer and links up with the chain of sub-surface atomic reactors. To save the planet, he intends to vent the cooling systems of each reactor through their output pipes and into the seas. Palgrave protests and says the coolant will react with the hydrogen molecules and create an enormous radioactive gas cloud that will rise over the oceans and suffocate the planet! Although every living thing will die, the Doctor says it would be preferable to letting the virus leave Poytee and spread throughout the known galaxy. Palgrave says such an action would be genocide, but Peri says it's just the lesser of two evils. She and the Doctor have to make these kinds of choices all the time. Palgrave refuses to let them do it and pulls a gun on the Doctor, so Peri smashes a vase over his head. As the planet starts to shake from the coolant reaction, the Doctor declares their work here is done. As soon as they get back to the TARDIS he thinks they should observe a moment's silence for the dead, and Peri agrees to make him a cup of tea.

Harom thinks Kettoo's version sounds closer to the mark, but there's still something that doesn't add up. It still doesn't seem credible somehow, and although Kettoo was certain she was right when she started telling the story, even she agrees that by the end she'd started to doubt herself. Harom wonders what's going on. They're supposed to be the Celestial Intervention Agency's top team, yet they can't even get their stories straight. Peri arrives with their desserts and Harom once again despairs at Kettoo's amateurish attempts to avoid any suspicion. The desserts have an added ingredient which Peri says will give it an extra kick. When she leaves, Harom tells Kettoo that her version was exaggerated and it's certainly not the way he recalls the incident. The Doctor's still guilty, of course, or else they wouldn't be here, and it's true there was a planet-wide infection, but how exactly did the Doctor deal with the problem...?

The TARDIS materialises inside the penthouse on Poytee and Peri is immediately impressed by the high-tech planet. The Doctor advises her not to touch anything until they know where they are and what the equipment does. They find a comms unit, and from the monitors they can see straight away that the people on the planet appear to be suffering from some form of mass hysteria. Palgrave arrives and assumes the Doctor and Peri have been sent by the Science Corps. He asks what information they have for him, but when he gets no response he tells them it doesn't matter as the exact cause of the illness is no longer relevant. He just hopes they'll be able to debunk the necessity for the Corps' latest plan to deal with the problem and come up with something less drastic. Palgrave reveals that their 'superiors' have decided to vent selective sub-surface atomic generators, control the spread of the resultant radioactive clouds using the climate modulator, then disperse them into the upper atmosphere once the situation has been dealt with. Peri realises this means mass murder and Palgrave says the Science Corps plans to implement it immediately. The Doctor asks if he can examine one of the victims first, so Palgrave agrees to take them down to the detention centre on level 15, but first they must stop off at the medical wing to pick up a syringe.

In the detention centre, Peri is horrified by the noise of the insane patients. The group stops at a cell and they watch as a woman, suffering from compulsive aggressive behaviour, repeatedly throws herself against the wall. Palgrave says they're all like this -- the people suffer from frenzied activity until they exhaust themselves into sleep and then it all starts again. In order to help her, the Doctor will need a blood sample, so Palgrave operates the door to the cell and then closes it behind him to reduce the risk of infection. As soon as the Doctor greets the woman, she attacks him and he's forced to come straight back out. Unfortunately the syringe got broken, but the Doctor now knows what the cause is. It's unmistakeably a variant of the Tuloz Virus and it's passed on by physical contact -- which means the Doctor is now infected too! The Doctor asks Peri to go with Palgrave to convince the Science Corps to stop their plans, while he will go to the laboratory and work in isolation on the climate modulator. But they must be quick -- they have a planet to save!

Finally, the three CIA members are in full agreement about what happened. It all seems so obvious now -- Peri persuaded the Science Corps to wait while the Doctor synthesised an antidote from his own blood sample and shot it into the atmosphere, where it was activated and dispersed across the planet using the climate modulator. The Doctor saved all those lives, so why in Rassilon's name were they thinking of killing him? Peri returns in time to see them finish their desserts and they're surprised when she addresses Co-ordinator Harom by name. She introduces them to the chef -- who is none other than the Doctor. The diners are confused, so the Doctor explains that in the course of gathering information from the planet Poytee for their report, they were all infected by a benign strain of the Tuloz Virus. It causes the sufferer to make wildly exaggerated claims, and this particular strain is responsible for something known as the urban myth, a story that may have at one point been based on some small truth but which has since lost itself to the realms of fantasy and scaremongering. The three diners agree this makes sense, but the Doctor reassures them that they've been slowly taking the antidote spread over their three-course meal and the infection has now been neutralised. Now that they can remember what really happened on Poytee, they will hopefully no longer want to kill the Doctor.