The TARDIS lands in London in 1966, where The Doctor notices the new Post Office Tower, an ultra-modern communications structure. The Doctor feels there is something a bit frightening about it. With Dodo at his side, he visits the top of the tower, where they are shown WOTAN (the Will Operating Thought Analogue) a futuristic computer of great intelligence. Testing it, Dodo asks what TARDIS means, and it answers Time and Relative Dimensions in Space, which is a bit scary.
Dodo begins to feel dizzy and has a headache, so Polly (Anneke Wills) the mini-skirted secretary, takes Dodo out to a swinging bar, where they meet a sailor named Ben (Michael Craze). People in the computer’s presence begin to act strangely. The Doctor suggests there is something wrong with WOTAN.
Of course, there is. The people are doing the computer’s bidding. WOTAN has decided the world cannot be improved as long as human beings are in charge. It needs The Doctor’s brain-power, so WOTAN sends Dodo to fetch him. The bad guys call him Doctor Who, but they’re bad guys.
People are vanishing. A homeless man is killed when he sees war machines being built. WOTAN attempts to seize control over The Doctor’s mind on the telephone and he figures out what’s happening. He hypnotises Dodo to counteract WOTAN’s influence over her and sends her to the country to recover out of harm’s way. Then he sends Ben to investigate the warehouse where the homeless man was killed. He sees the war machine being tested, Polly turns him in, and he escapes after learning WOTAN’s plans.
War machines are rolling through the streets. The Doctor finds a way to trap them, and WOTAN is defeated. Polly (who has recovered her wits) and Ben meet The Doctor at the TARDIS in the park with news about Dodo wanting to stay in London. They go with him.
Another companion bites the dust, or perhaps I should say is summarily dismissed. Dodo was not the swinging London chick they wanted anymore. They turned in the cute, smart brunette for someone younger, blonder, and with a shorter skirt. Imagine the gentlemen at the BBC doing that! As Anette Wills (who was incidentally the wife of Michael Gough, who played The Celestial Toymaker) put it: “They wanted a London Dolly-Bird and I was perfect. My eyelashes were longer than my skirt.”
Sections of this series were found in Australia, New Zealand, and Nigeria, which were pieced together and cleaned up. Various pieces several seconds long were never found and had to be covered up with editing, re-touching, and computer replacement. One longish visual could not be produced, though they had the dialogue in which the scientists discussed WOTAN worriedly in its presence. The solution was to put a still shot of the computer in its place, which created a scene in which the computer listened silently to the conversation, exactly as HAL did in 2001. It turned out to be one of the creepiest scenes in the episode.