The TARDIS materialises in central London, Fitzroy Square. It is 1966 and Dodo is thrilled to be home. She and the Doctor have little time to look around before they spot a policeman approaching. The Doctor produces a sign reading "out of order" and hangs it on the front of the TARDIS. The Doctor fears that the ship may be mistaken for a real police box in this time and place. He "forgets" to mention that Dodo did exactly that when she first found the ship. The policeman approaches but moves on when he sees the sign.

The Doctor notices a very tall cylindrical building towering over the landscape. The Post Office Tower. Dodo is surprised to see that it is now finished and is impressed at its modern beauty. The Doctor, however, has become highly agitated, sensing something "alien" about the tower. Something very powerful. His hand shakes and he complains of a prickling sensation in his skin. The last time he felt something like it, the Daleks were near. Dodo doesn't understand what Daleks are or what is worrying the Doctor. She must run to catch up when he hurries off toward the tower to investigate.

In an office near the top of the tower, a scientist - Professor Brett - goes over some notes with his secretary, Polly. The office has an expansive view of London far below, but that is not the focal point of the room. The most dominant feature is a giant computer. Six banks of control panels, instruments, and recording devices make up the giant machine. It hums and flashes constantly, almost as if talking to itself. It seems somehow alive in the room.

Brett's security officer, Major Green, escorts the Doctor and Dodo into the office. Brett seems glad of the interruption, an opportunity to show off the computer which is the culmination of his life's work. The Doctor has presented himself as somewhat of an expert in computers. When he sees the machine in the corner of the room, he is certain it is what he felt outside - an enormous energy source almost magnetically drawing him in.

Professor Brett explains that this computer is the most advanced in the world. It is called WOTAN, an acronym for Will Operating Thought Analogue, and it will soon be linked up with all other computers in the world as a sort of central intelligence. It is a superior problem-solver capable of millions of complex calculations far in excess of human beings. In fact, WOTAN is the first machine that can think for itself and, says Brett, it never makes mistakes.

The Doctor is extremely sceptical of these claims and so decides to test the machine for himself. Using a voice command, he asks WOTAN for the square root of 17422. When the machine prints out the correct result almost instantaneously, the Doctor must admit he's impressed. But Dodo too wants to test WOTAN and sets it a much more difficult problem. She asks it to explain the word TARDIS. The Doctor's astonishment, the response is correct.

Brett notices that Dodo is now staring intently at WOTAN and she doesn't respond to his voice. He spins her round and she moves unprotestingly, almost hypnotised. The Doctor's voice snaps her out of it and she complains of a buzzing in her ears. Polly takes her aside to make sure she's all right while the Doctor questions Brett on WOTAN's operating principles.

Dodo is soon better and chatting casually with Polly. The two are very close to the same age, yet Polly seems much more sophisticated and "with it". Dodo complains that she feels "out of it" here in London, which is the truth of course. She's been gone for some time. Although she's not far from when she left, things have changed rapidly in this modern city. What Dodo would really like is to visit the hottest night spot in town. Polly is glad to oblige. She will take Dodo to her favourite hangout - The Inferno.

That evening, Polly leads Dodo to Covent Garden and to a subterranean club teeming with young people dancing. The décor is modern cavern and the music is loud guitar pop. Dodo seems pleased. Polly introduces Dodo to the proprietor, a young woman called Kitty. Kitty tells Polly she has a problem that only Polly can solve. She reminds Polly about a young sailor she met here last week. Since that day, the young man has returned nightly only to sit moping at the end of the bar, saying nothing and bringing everyone down. Polly doesn't especially remember the young man but - as if on cue - recognises him as he enters through the crowd.

The sullen young man goes directly to the end of the bar and sits, his head in his hands. Several people move away from him as he does. Kitty asks if Polly won't go and cheer him up, just to help the atmosphere of the club. Polly, ever-cheerful and up for a good time, agrees and drags Dodo on her "rescue mission". Polly engages the young sailor in conversation but he doesn't seem interested in talking. He vaguely remembers her from last week and Polly pretends to be stung by this. She chides him for looking so sad and managed to coax a smile from him.

The sailor explains that he's got a 6-month shore posting while his ship is off to the West Indies and that's why he's glum. Polly cracks wise and the sailor reacts with a biting retort. He doesn't really mean it, but it's enough to put Polly off and she leaves, saying the young man has no sense of humour.

As Polly tries to move off, she is intercepted by another man, known as Flash. He appears to be drunk and has overheard her conversation. He claims to have "a great sense of humour". He corners Polly and continues to chat her up aggressively, despite her requests for him to leave her alone. The sailor comes to her aid and the two men verbally spar until the sailor has had enough and he tosses Flash to the floor. A brief scuffle ensues but Flash is no match for the sailor. Kitty hurries over and Flash is encouraged to leave immediately.

The sailor blames Polly for "encouraging" Flash and she reacts with anger, but Dodo smoothes things over, thanking the sailor for his help. He introduces himself as Ben Jackson.

Elsewhere in London, the Doctor arrives at the Royal Scientific Club, site of the press conference to announce the impending link up between WOTAN and the world's computer systems. The briefing, being led by Club leader Sir Charles Summer, is already underway when then Doctor enters. The gathered reporters are concerned that the computer link-up, scheduled to take place in 4 days' time, will give enormous power to the people who run WOTAN. But Sir Charles assures them that WOTAN thinks for itself, has no emotion or imaginative power to get in the way, and issues only "the truth".

There is some fear that this wonder-machine can seemingly do without humans. Sir Charles brushes this aside, but the Doctor seems very worried over this idea.

Sir Charles, too, is worried but for a different reason. Professor Brett is a no-show for his own press conference. Brett's assistant, Professor Krimpton, has no idea where he is and Sir Charles must make apologies to the gathered press.

In his office, Brett has been delayed by a phone call. He finally manages to brush off the caller and begins to leave, but instead calls in Major Green. Brett believes there is someone at large in this part of the building. He's been keenly aware of someone watching and listening to him all day. Green assures him that security is too tight for anyone to slip through and Brett apologises for imagining things. He chalks it up to overwork.

However, as Green goes out, something strange happens. The odd mechanical hum that pervades the office - the sounds of WOTAN's operations - changes in pitch and intensity. It begins boring into Brett's mind, causing him some pain. Brett tries to leave but the sounds become louder, deeper, and more insistent. He cannot move and soon cannot resist. He is dragged back toward WOTAN's main control panel where he stops. He addresses his question toward the computer itself, totally subservient: "What do you want?"

Back at The Inferno, Ben has come completely out of his funk and is burning up the dance floor with Polly and Dodo. He and Polly have overcome their initial antagonism and seem to be getting along quite well. He even teasingly calls her "Duchess", a comment on her supposed debutante manner. Dodo complains of a persistent headache - a high-pitched humming in her head which she's had since she left Brett's office. As Ben and Polly head back for another dance, Dodo stays behind at the bar rubbing her temples and looking very distant.

Professor Brett bursts into the press conference, shouldering through the crowd of reporters and refusing to answer any questions, even from Sir Charles. He wants Krimpton and he physically drags the man out of the room. The reporters follow, trying to find an answer to Brett's brusque behaviour. The briefing is over.

Sir Charles introduces himself to the Doctor and the two of them puzzle over what has just happened. Sir Chillers suspects there may be something wrong with WOTAN, which would explain why Brett wouldn't answer any questions, and he goes off to try and find an answer. The Doctor, however, is very sceptical of this explanation.

Major Green stops by Brett's office to check on security and finds himself under the same mental attack as Professor Brett. He succumbs to the sounds and is completely servile. In response to a command heard only by him, Green dials the telephone.

The call goes to The Inferno of all places. It is for Dodo and Kitty goes to fetch her. As soon as Dodo picks up, Green switches the call through WOTAN itself. On her end, Dodo flinches as an intense sound fills her ears. After a moment, she relaxes and gazes blankly as if hypnotised. Without a word to her new friends, Dodo leaves the club as if sleepwalking.

Krimpton is tired of being manhandled by Brett and breaks free from his grip as they enter the lift at the base of the Post Office Tower. He demands to know what is happening. He fears that WOTAN has broken down, but Brett tells him it is "we who have broken down; we who have failed". He tells an astonished Krimpton that development of the Earth is at a standstill and can go no further under the direction of mankind. That is the conclusion reached by WOTAN.

Krimpton can barely hide his disdain as he follows Brett into his office. Brett says WOTAN will take control of the Earth and mankind will serve. If mankind refuses, it will be eliminated. Krimpton cannot believe what he's hearing, especially the deadly seriousness of Brett's tone. He's convinced that Brett is mad and turns to leave. But his way is blocked by Major Green. There is no escape.

Before he can phone for help, Krimpton comes under mental attack from WOTAN, the sounds invading his brain and rendering him unable to move. He tries to resists, invoking the superior will of humanity, but he eventually succumbs to the will of WOTAN. He is now a slave to the computer, like the others.

At The Inferno, Ben and Polly have noticed Dodo's absence. No one saw her leave and they become worried. The Doctor arrives and approaches Polly. He meets Ben and Kitty as well, but his main concern is Dodo. An anguished Polly tells him of the telephone call and her abrupt disappearance.

Brett announces to his comrades that WOTAN requires one very special human brain in order to enact its plan. The task of leading that person here is to be left to another of their group. Brett welcomes Dodo to the office. She comes forward to ask the computer for instructions.

With no further audible instructions, Dodo leaves to complete her task. Professor Brett announces that WOTAN's takeover of the world will take only a few days. WOTAN has decided that London is the first world capital to be taken over, followed by Washington and Moscow. To effect the takeover, War Machines will be built at strategic points in London. While Major Green searches out suitable locations, manual and scientific labour will be recruited by the others using the same telephone thought control method employed on Dodo. Professor Krimpton will be responsible for the design and programming of the War Machines - mobile, self-powered computers which will carry out WOTAN's will. But first, the Doctor must be brought into WOTAN's service. It must be tonight.

At The Inferno, the Doctor and his new friends are very worried. It is early in the morning now and there is still no sign of Dodo. Polly thinks they should at least phone the hospitals to make sure she hasn't had an accident, but before she can do so, Dodo arrives acting as if nothing has happened. She concocts a story about having gone to see an old friend - who called her at the club - but is vague about the details in the face of the Doctor's questions. However, he's glad enough to have Dodo back safely and he heads out to try and hail a cab. They are to stay with Sir Charles Summer and his family tonight.

Ben and Polly leave at the same time and go off to fetch a taxi for the Doctor. Dodo is acting antsy with all these others around. Unbeknownst to any of them, they are spoiling her plans. Hiding in the shadows nearby are a group of shady-looking men, one armed with chloroform, waiting to capture the Doctor and take him to WOTAN. Dodo tries to lure him toward them, saying there is a taxi in that direction, but a cab arrives momentarily, directed here by Ben.

A scruffy vagabond exits the taxi and he offers the driver a grubby pound note for the fare. The driver doesn't have change and the two have words. The Doctor gets irate at the delay and Polly comes to the rescue with change. The vagrant is free to go.

Polly piles in with the Doctor, as does a disappointed Dodo. Ben is going to kip at a services club around the corner and stays behind. The cab heads off, but not before Polly asks Ben to meet her at the Post Office Tower for a lunch date tomorrow. The two seem a matched pair, despite their rocky beginning.

As the cab speeds off, Ben notices the vagrant standing by and inquires whether he's got a place to sleep for the night. He says he'll stay in the old warehouse next door - a veritable paradise compared to other places he's been. Recently. The two men go their separate ways.

One of the men who were waiting for the Doctor calls into Major Green and reports their failure. There is still a contingency plan. The man rings off and enters the old warehouse where his compatriots have already gone. Inside, work is already in progress for the construction of a War Machine.

WOTAN's minions have worked remarkably quickly, assembling a large labour force in just this one location alone. Parts have been shipped, a plan has been finalised, and Brett himself oversees the first stages of construction. The operation is impressive indeed, working to a precise plan created by WOTAN.

The vagrant enters the warehouse despite all the noise he can hear from inside. He's curious, to be sure, but also a little miffed that his new home seems to have been invaded. He is astonished by what he sees - dozens of men working with machines and tools to construct... something. Professor Brett, issuing orders by microphone direct from WOTAN, receives word of an intruder in the warehouse. He calls out the vagabond's precise location and despatches a group of men to find and contain him. This strangers is seen as a grave threat.

The vagrant tries to run, but the computer-controlled drones find and trap him. He tries to bargain for his freedom, promising to say nothing about what he's seen. But he's so overwhelmed by the sights and activity around him - the computers, machinery, and well-drilled labour force - that he will clearly not keep his promise. Realising he has stumbled onto something evil, he tries to run again. But he is caught and the threat is "eliminated".

Brett encourages the men to get back to work at once. Construction on this War Machine must be completed by the morning. And, judging from the tall tank-like metal shell already partially built, that goal will be easily achieved.

The next morning, the Doctor peruses the newspaper at Sir Charles' home. There is a story about the death of the vagrant whose body was found dumped at Covent Garden. Cause of death unknown. The Doctor recognises the man from the taxi and becomes worried, although he can't quite articulate his concern.

Sir Charles, however, has a real problem. Two very vague resignation letters have arrived from prominent scientists on his faculty. No reasons are given for their sudden departure and no one has seen them since last night. Unbeknownst to them, the men have gone to join WOTAN. The Doctor has no answer for this extraordinary event and returns to the newspaper, turning over this information in his mind. Both he and Sir Charles are baffled when Polly arrives, sent by Major Green. She was told that Brett didn't need her today and that Sir Charles' secretary was ill. The oddest part is that Sir Charles' secretary is indeed out, although there's no way that Green could have known.

Dodo comes in, acting quite odd and practically orders Polly to get to work. She was the source of Major Green's information, although no one else has yet realised this. Dodo listens in while the Doctor and Sir Charles resume their conversation about the missing computer scientists. Seizing the opportunity, she suggests contacting Professor Brett for help. The Doctor agrees this might work - noting Dodo's unusual eagerness to be involved in this - and decides to phone Brett. Dodo encourages this happily.

Brett is pleased at the unexpected call and Krimpton switches him through direct to WOTAN. The Doctor's brain is assaulted by the mind-controlling soundwaves and he staggers as if electrocuted. He drops the phone and collapses into a chair, moaning in agony. Sir Charles hurries to fetch water while Dodo attends to the Doctor. Believing him now to be a fellow servant of WOTAN, she begins to tell him about construction at "strategic points in London" but is stopped when the Doctor begins speaking.

In awestruck and fearful tones, the Doctor explains that he felt as if something were trying to absorb him. Something enormous and evil. But it quickly becomes clear that he has resisted it and is not obeying orders from WOTAN. Now it's Dodo's turn to be afraid. As Sir Charles and Polly enter with water, Dodo tries to slip out. The Doctor announces a deadly danger centred in the Post Office Tower, sees Dodo leaving and stops her. She stands as if hypnotised, responding to the Doctor's instructions like a sleepwalker.

The Doctor uses his voice and his dark-jewelled ring to put Dodo to sleep, cancelling out the instructions previously implanted. He predicts that she will be fine when she wakes, but stresses the need for peace and quiet. Polly, worried over what she has learnt, slips away while the Doctor and Sir Charles decide to send Dodo to Sir Charles' country house to rest and recover. They notice Polly's absence, but the Doctor is more concerned over Dodo's ominous words and what they may mean.

More spare parts and electronics arrive in London for construction of the War Machines. In the Covent Garden warehouse, the War Machine is nearing completion. It is a 2-meter-tall metal tank on tracks. It is rectangular with sharp corners, an aerial on top, and a computer bank on one side. It has two massive arms with ram attachments at the ends and two nozzle-like protrusions in the front. It's "face" contains one enormous horizontal eye, some flashing lights, and a powerful beam that it uses to see clearly. The machine emits a computer hum just like WOTAN. It is an extension of WOTAN.

Major Green now oversees the work here, including the fitting and testing of the War Machine's offensive weapons. He orders one of the labourers to stand still on one side of the room. Using voice command, Green directs the machine toward the man. It moves under its own power, gliding smoothly. It aims one of the nozzles and fires a thick burst of smoke at the man. He collapses immediately.

Test satisfactory.

In Brett's office, WOTAN reiterates its assertion that "Doctor Who is required" and that he must be brought here. Krimpton speculates that Dodo has failed but WOTAN only repeats its instruction insistently. The conversation is interrupted when Polly enters. She is very concerned over her employer's safety...until she gets one look at the evil fire in his eyes. Then she becomes very frightened indeed. The doors behind her are now closed and she is trapped in the office.

The Doctor, absorbed in the clues to this mystery, is startled by the arrival of Ben Jackson. He's come looking for Polly, who did not show up for their lunch date. He heard that she came here this morning. The Doctor is more concerned than ever about Polly, but first things first. He asks the young sailor if he read about the death of the tramp in Covent Garden. Ben has and he remembers the man from the club last night. The Doctor wishes to investigate this area to satisfy his vague worry. Ben agrees to look around for him and hurries off. Both he and the Doctor hope that the tramp's death and Polly's disappearance aren't connected.

Ben sees nothing unusual in the bustle of activity at the Garden, but as he passes by the warehouse next door to The Inferno, he hears amplified voices. Knowing the place should be deserted, he becomes curious and goes inside. He just misses seeing a test of the crushing arms of the War Machine, but is nearly caught up in its vision test. Ben can hardly believe what he sees as he crouches behind some boxes. The machine is enormous and powerful, responding immediately to commands.

He watches as the machine undergoes a movement test, traversing the warehouse floor and using its heavy metal arms to smash through all obstacles. As it goes, it seems to be moving even more independently. Major Green gives it no orders yet it seems to have a sudden purpose in its movements.

Ben dodges and runs for the door, fear overtaking him. The War Machine does not pursue, a wall of boxes marked "high explosive" blocking its way. Major Green halts work and orders his labourers to search for the intruder.

Ben makes it through an inner doorway and heads for the outer door, but stops dead in his tracks when he sees Polly before him. She sees unnaturally calm and says she's come looking for him on instructions from the Doctor, but that is not quite the truth. She is now one of WOTAN's servants. Ben, nearly hysterical, tries to get her to leave with him, explaining the madness he's just witnessed. But she will not go with him. In fact, she wants to continue inside.

Green gets word via WOTAN and the War Machine that Ben is in the entryway. The searches are diverted and he orders all outer doors to be locked.

To Ben's horror, Polly obeys the order and locks the outer door, saying she cannot let him escape. He tries to physically restrain her, but she moves as if possessed, single-minded in her determination to keep Ben inside. The delay is just enough time for Green's men to enter and capture Ben. They drag him back into the warehouse, kicking and screaming. He begs Polly to escape and get he Doctor, somehow not knowing (or not wanting to believe) that she is in league with the villains in the warehouse. He continues to call to her for help as he is dragged before Major Green. Green is ready to let the War Machine despatch the spy.

Back at Sir Charles' house, the Doctor is becoming worried over Ben's extended absence. He feels that the lad is dependable and he cannot explain why Ben has not at least called. Sir Charles suggests calling the police, but the Doctor fears their involvement will drive this shadowy threat further underground. He must hope that Ben is all right and will return with information.

Major Green denounces Ben as a threat to "mechanised evolution" - the takeover of man by machines. He must be killed. However, Polly intervenes before the War Machine can be set loose on him. She says that labour is still needed to ensure victory and that Ben should be spared and forced to work. WOTAN needs all the labour that can be mustered. Green agrees and all the slaves return to work.

Ben is grateful for being spared, but he is disappointed to learn this wasn't a ruse on Polly's part. He has realised that she is a brainwashed follower of WOTAN and she will force him to work toward the victory of the War Machines.

In Brett's office, plans continue for the takeover. The War Machines will be programmed to attack at noon tomorrow, all working simultaneously to occupy strategic centres and to assume authority over humans. They are programmed to destroy all forms of life that oppose them, but final command programming is still incomplete. The Covent Garden machine is closest to completion, on its final test. Brett and Krimpton prepare for victory.

Back at the warehouse, the endless hours of continuous work are beginning to show in WOTAN's human slaves. Several are at the point of exhaustion, working until they literally drop. Green urges them on, collecting and storing masses of weapons and explosives for the battle to come. The work continues right around those who drop due to weakness. More will follow.

Also nearing exhaustion is Polly. Ben shows concern for her, but she only repeats the mantra of victory for the War Machines and carries on. Ben learns from her about the attack planned for noon tomorrow just before he notices that there is no longer a guard on the outer door. Everyone is absorbed in the work at hand and they seem to have forgotten that one of their labourers has not been brainwashed. Now is Ben's chance to escape.

He heads for the door, unseen by anyone...except Polly. Their eyes meet and there is a long pause. Will she give him away? She could easily sound the alarm and he would be stopped dead. Instead - miraculously - Polly returns to work. Ben wastes no time. He has to get out and warn the Doctor. It's the only way to stop these madmen and to save Polly. He must use a crowbar to pry open the outer door, but he manages to do so without anyone hearing and he races outside.

Ben wastes no time in reaching Sir Charles' house, out of breath and half-crazed with fear. The Doctor listens intently to the story of Polly, the warehouse, the computer-zombies, and the killer machine primed to take over London.

Major Green notices Ben's absence and questions Polly, as she was responsible for him. Polly admits he escaped and that she did nothing to stop him. Her conditioning seems to lapse for a moment as she recalls Ben as a friend. Green tells her she has no friend, no life other than to serve WOTAN. He orders her returned to WOTAN for punishment.

Sir Charles is hard-pressed to believe Ben's story but to the Doctor it all ties up. Ben derides Sir Charles for his stubbornness, but it is the Doctor's steadfast support of the story that finally convinces Sir Charles. He decides to call the police. Ben thinks this inadequate, even though there are only about 20 people at the warehouse. The machine could easily stop the police. The Doctor thinks there is even more to consider: the fact that this is not the only one of these machines. There are more and they can't be stopped individually. He says they must strike at the heart of the menace: WOTAN.

Sir Charles steadfastly refuses to accept that WOTAN is connected to the War Machine and goes off to contact the Minister of Defense to ask for an attack on the Covent Garden warehouse. Ben and the Doctor head off to the warehouse on their own while Sir Charles relays details to the Minister. He, too, decides to bypass the police and go straight to the Army. Sir Charles agrees with this plan and heads off to Covent Garden himself.

Several Army units are quickly despatched to the warehouse and a cordon is thrown up around it. Sir Charles takes the lead in the enterprise, having come to the realisation that this is perhaps a larger threat that first thought. When he is convinced that all is in readiness, he orders a patrol to enter.

Orange Patrol is to reconnoitre and report...and to "be prepared for anything". They head inside, armed and ready.

Major Green detects a large amount of unusual electrical activity outside the warehouse when it interferes with his electronics. He alerts everyone in the warehouse and sends the War Machine to investigate. When the machine locates the soldiers, he orders an all-out attack.

The machine fires its smoke weapons and chaos erupts. WOTAN's human minions attack as well and the soldiers are in over their heads. One soldier is killed by the War Machine and the rest find their weapons useless, jammed by impulses from the machine. The embattled soldiers must fight hand-to-hand with their robot-like attackers in close quarters, all the while being fired upon by the War Machine. They are outnumbered and overwhelmed and are at last forced to retreat.

The Doctor and Ben arrive at the command post just as the corporal in charge of Orange Patrol returns. He is nearly hysterical and incoherent. He manages to point out the oncoming War Machine as it bursts from the warehouse to attack the soldiers outside.

The machine rolls down an alleyway, smashing everything in its path and setting fire to debris with its smoke weapon. The soldiers on the cordon are dumbstruck by its awesome evil and power. When they do recover themselves, they are unable to retaliate as their guns and grenades are jammed. Sir Charles tries to reason with the machine's controllers in the warehouse via bullhorn. It is clear that he does not realise the scope of the peril they face. The machine lumbers ever closer to the command post and the soldiers are forced to fall back.

The corporal begs Sir Charles to leave for his own good, and he is forced to comply as the machine looms closer. Sir Charles, Ben, and the soldiers back away, leaving only the Doctor. He actually takes a defiant step forward, directly into the path of the awesome War Machine.

Ben, thinking something is wrong with the Doctor, runs to grab him and drag him from the path of the lumbering War Machine. But the Doctor stays put, watching the machine intently. One of its heavy arms raises up as it approaches the Doctor, but inexplicably the machine stops dead and lowers its arm. The Doctor is safe.

A news report goes out almost immediately, announcing that the War Machine has been put out of action, cancelling the previous warning of an emergency. High level government meetings are underway, but a bulletin explains that further attacks from War Machines can be expected.

The Covent Garden task force is graced by the presence of the Minister of Defense, an impatient bureaucrat who is looking for answers. The Doctor and Sir Charles explain that the War Machine stopped in its tracks because it was not fully programmed. It was put into action sooner than its masters planned due to the arrival of the Army. The Doctor calls it luck, but doubts that they will be so fortunate next time.

Elsewhere in London, a second machine has been completed. Testing will commence immediately and no delays will be tolerated by WOTAN.

Ben reports to the Doctor that Polly is not among the prisoners taken from the warehouse. He is very concerned, but the Doctor has his hands full examining the War Machine and refuses to discuss it. He hands his cloak over to Ben so he can work more easily. A key falls out of the cloak's pocket but the Minister arrives before Ben can return it. Disgusted, Ben pockets the key and hurries off as the two men talk.

The Doctor has succeeded in decoding the computer programming for the machine. There are 11 similar machines in London, within a 20-30 mile area. They are all programmed to attack at noon today. The Minister is worried indeed by this news.

The second War Machine begins its motive test under relayed instructions from Professor Brett, moving as commanded. However, the machine suddenly attacks the communications unit and smashes it, cutting off contact with Brett. The machine fires its smoke weapon and kills the technician on duty, then it rolls away. Something has gone haywire with this machine.

Brett and Krimpton, in the Post Office Tower, receive this information and hurry to try and correct the machine's programming.

Major Green, the ringleader of the Covent Garden warehouse, is brought forward for questioning. His hypnotic conditioning has worn off and he does not know where he is or how he got there. The Doctor tries to jog his memory, but Green doesn't even recognize the War Machine he helped build. He is taken away for medical attention.

Everything has now fallen into place for the Doctor. WOTAN is clearly behind all of this, and Professor Brett is the leader of the computer's human minions. Sir Charles advocates storming the Post Office Tower, but the Doctor believes that strong-arm tactics will not succeed. He must think of some other way.

The renegade War Machine is now loose on the streets of London. It attacks and kills a man in a phone box, but not before he can call in a tip to the police. Soon news of the second machine is all over the radio and television.

Ben is more concerned than ever about Polly, afraid she's been sent to another of WOTAN's construction sites. The Doctor has too much on his mind now to worry about one person but Ben won't give up on the person who saved his life in the warehouse.

The War Machine continues its reign of terror and is now approaching the Battersea Power Station. Sir Charles passes this news to the Doctor and looks to him for an answer. He decides that it is electromagnetism not firepower that they need to stop this menace. The Doctor plans to capture the War Machine.

Polly returns to Brett's office as ordered, to submit herself to WOTAN's judgment for letting Ben escape. Brett and Krimpton assure her she'll be dealt with in due course, but for right now they need her help to subdue the errant machine.

The Doctor has drawn up plans for an electromagnetic trap, an elaborate and difficult construction. Even if it can be built in time, Sir Charles worries that they still can't contain the mighty machine. The Doctor obtains a map of the West London area being traversed by the machine and orders three sections of road closed down. This way, the machine will be forced into a dead end where it can be more easily trapped.

The streets are closed and emptied of people while the Army engineers and soldiers construct a sort of electromagnetic corral in the cul-de-sac. Two rows of cables create a 4-square perimeter fence.

At the new command post, the Doctor explains they must prepare the cables on 3 sides and the square corral and leave the 4th side (facing the street) open. They must then lure the machine into the corral and connect the 4th set of cables behind it. Sir Charles thinks this extremely dangerous, as does Ben. He bravely offers to connect the cables himself when the time comes.

The Army takes up positions all around the area and Ben gets into position next to the corral. The War Machine appears at the top of the street and begins descending the cobbled lane, its smoke jets flaring and its metal arms flailing. The machine reaches the edge of the electromagnetic corral and stops. It looks for a moment as if it has sensed the trap and won't go in. Ben and the antsy soldiers must wait for a long harrowing moment nose-to-nose with the evil machine. At last, it moves forward slowly and into the centre of the square of cables.

Ben connects the last one and the Doctor orders the current switched on. The War Machine's ever present computer hum changes pitch and it is quickly clear that it is truly trapped, unable to break through the cables. Its arms and weapons are still as the Doctor enters the corral. The machine reacts slightly to his presence but he is safe. A moment's tinkering and the mighty War Machine is "neutralised". The Doctor has succeeded.

Word goes out all around the world of this latest victory. But the question on everyone's mind is the same: can the other War Machines be stopped before noon?

The errant machine is quickly shipped to Covent Garden where the Doctor performs some hurried modifications to its programming. He says he's changed its character and hopes the machine, once reactivated, will obey the new commands he's fed into it. Ben has the honour of reactivating the War Machine and everyone but the Doctor stands well back when it returns to life. The Doctor says it's quite safe and stays put. The machine bypasses him completely and heads off down the street. It is on a new mission, one of the Doctor's devising.

The Doctor explains that "his machine" is heading to the Post Office Tower and to Brett's office. It is programmed to face down WOTAN and it must do so before noon. Ben becomes concerned as he fears that Polly may be with Brett. Afraid she will be caught in the middle of events there, Ben hurries off, trying to beat the machine there. The Doctor now fears for both his friends' lives.

The War Machine hurries on its way, stopping for nothing. But there are only 11 minutes left until noon.

Brett and Krimpton are aware of the nearness of their attack deadline and send stand-by orders to all War Machine crews. However, WOTAN says it will give the final order itself.

The streets are deserted as the War machine speeds toward the Tower. Not far behind, the Doctor, Sir Charles, and the Minister ride in a car. The Doctor describes the coming conflict between his machine and WOTAN like the crossing of two electrical currents. Cataclysmic. If he is successful, all those under hypnosis will be released when WOTAN is destroyed.

The War Machine enters the reception area of the Tower.

Miraculously, Ben has managed to arrive just before the machine. He bursts into Brett's office and begs Polly to leave with him. She wishes to stay with WOTAN for the glory of the machines and neither she nor the others believe him when he says WOTAN's power is finished. But suddenly danger registers on all instruments and a second computer hum fills the room. Ben grabs Polly and strong-arms her toward the stairs as the Doctor's reprogrammed War Machine enters.

Brett and Krimpton do everything in their power - forced by WOTAN's commands - to stop the machine. WOTAN itself orders the machine to stay back. But the machine fires its smoke weapon indiscriminately. Krimpton is killed and WOTAN's Central Processing Unit is destroyed. The War Machine itself succumbs and explodes as well.

Professor Brett is released from mind control and stares blankly around. He is horrified by the destruction and by Krimpton's lifeless body before him. What on Earth has happened?

The Doctor, Sir Charles, and the Minister enter the smoke-filled room and survey the damage. Sir Charles can't quite make sense of it but the Doctor assures him that the threat is over. All the other War Machines are immobilised, waiting for orders from WOTAN. Orders that will never come.

Sir Charles goes to make sure that Brett is all right. Physically he is fine, but he has many questions. Sir Charles turns to the Doctor, only to find that he is gone.

A short time later, the Doctor waits impatiently outside the TARDIS in Fitzroy Square. He is waiting for Dodo and is very restless. He is just about to go inside, presumably to leave, when Polly and Ben race up. They are no worse for the wear of their adventures and they bear a message from Sir Charles about Dodo. She is feeling better but would like to stay here. She sends her love.

The Doctor is somewhat put out by this abrupt departure, mumbling under his breath about all that he has shown her in time and space. But he realises that he isn't making sense to Polly and Ben and so sends them off with a cursory good-bye.

The two young people step away but turn to watch as the strange old man produces a key that opens the police box. He takes the "out of order" sign with him as he enters. Ben suddenly remembers the key that the Doctor dropped earlier. He still has it. Polly snatches it from him, intending to return it to the Doctor.

Ben is concerned as he has to be back in barracks for his shore posting very shortly, but Polly is determined to return the key. There is perhaps more than a curfew worrying Ben. Perhaps it is a fear of tampering with the unknown. Whatever, he is unable to stop the curious Polly from inserting the key and opening the door. After a second's hesitation, he follows her inside and closes the door.

The TARDIS dematerialises a moment later, whisking Ben and Polly off on unknowable adventures.