You're an evil man, Vaughn. You're sadistic. You're a megalomaniac. You're insane. I pity you. But if I get half a chance, I'll kill you.
— Professor Watkins tells it like it is.
The TARDIS arrives in London in the near future, the Doctor and companions are enlisted by Isobel Watkins to find her father, a computer scientist working for International Electromatics.
IE's director, Tobias Vaughn, arouses the Doctor's suspicions - confirmed by meeting Lethbridge-Stewart again (see "The Web of Fear
"), recently promoted to Brigadier, who says that numerous other IE staff have gone missing. Lethbridge-Stewart now heads the British arm of UNIT, the United Nations Intelligence Taskforce, charged with investigating alien sightings and other such things.
The Doctor discovers that Vaughn is acting on behalf of the Cybermen, who plan to invade Earth, but is also planning to double-cross them and seize power for himself. The Cybermen send a hypnotic signal through all IE-made equipment, immobilising most of Earth's population, and start emerging from London's sewers to take over. However, the Doctor has managed to protect himself and the others from the signal and succeeds in defeating the invasion, thanks in no small part to Zoe's phenomenal brain, plotting guidance trajectories for nuclear missiles to destroy the incoming fleet.The Invasion
presaged the shape of many Doctor Who stories to come, featuring an alien invasion of Earth aided and abetted by a corrupt industrialist, with UNIT providing cannon fodder and the military connections to fight back.
- Affably Evil: Tobias Vaughn. Very courteous, even to trespassers, as long as one is not hindering his plans. But when he gets upset...
- Animated Adaptation: The two missing episodes were remade in an animated format for the DVD release.
- Corrupt Corporate Executive
- Cut and Paste Environments: The same set is used for Vaughn's office in two different buildings (with a different view out of the window). Lampshaded.
- Cybernetics Eat Your Soul: Averted. Unlike the usual plot scheme, Vaughn is positively thrilled to have been given a cyborg body, and doesn't lose any of his personality.
- Early-Installment Weirdness: Benton dresses in plain clothes and UNIT acts like a typical TV 60's international spy organisation, rather than the British military unit it became established as in the John Pertwee years.
- Also UNIT using sensible tactics and weapons to defeat the Cybermen (throwing grenades or using bazookas rather than just firing their rifles ineffectively). By their next appearance they've decayed to an army of redshirts.
- Evil Is Not a Toy
- Expy: Professor Watkins and his niece Isobel stand in for Professor Travers and his daughter Anne who had appeared earlier. The did not want to pay the writers of the earlier characters. Also possibly the sewer-lurking Cybermen for the subway-lurking Yeti — there's a rumour that this story was originally planned as a direct sequel to "The Web of Fear", before the writers of the two previous Yeti stories fell out with the showrunners over the editing of "The Dominators" and the IP ownership of the Quarks.
- For Inconvenience, Press "1": Written in 1969, a rare example of Doctor Who predicting the future effectively.
- Genre Savvy: Vaughn has prepared the emotion machine in the quite likely event the Cybermen will turn on him and even wants to take the TARDIS in the event that his deal with the obviously untrustworthy monsters goes south and he has to get away.
- Getting Crap Past the Radar: Vaughn isn't exactly clear on what Packer will do to Isobel or ZoŽ if they're turned over to him, but it's as strongly implied as it can be in Doctor Who they'll be raped.
- Idiot Ball: Zoe, mainly to annoy Jamie, agrees to Isobel's insanely dangerous plan of photographing the Cybermen. Unlike Isobel, she's encountered the Cybermen before and ought to know better.
- Immune to Bullets: Vaughn, thanks to voluntary partial Cyber-conversion.
- Kidnapped Scientist: Professor Watkins.
- Large Ham: Viewers may remember Kevin Stoney from his former role as Mavic Chen. His hamminess has seen no decrease whatsoever.
- Magic Skirt: Well, kilt - the girls' skirts definitely don't do this, but Jamie's kilt stays in place. It's not magic, though - it's weighted.
- Modesty Shorts: A photograph taken while filming shows Sally Faulkner (Isobel) wore shorts under her dress for the scene where she's rescued by the helicopter. The animators reconstructing that sequence had other ideas.
- Multinational Team: UNIT
- Panty Shot: The two girls start in very short dresses (Isobel was shooting pictures using Zoe as a model) and stay that way for three-quarters of the episode - which does not make running from a private army or climbing up and down ladders easy to do modestly. They fail.
- Rank Up: Colonel Lethbridge-Stewart is now The Brigadier.
- Redemption Equals Death - Vaughn. Well, sort of, since he claims he just wants revenge.
- Stock Episode Titles: 40 uses
- Surrounded by Idiots: Vaughn has his incompetent henchman Packer — unusual given his stated desire for efficiency.
- Talking The Computer To Death: Zoe! Vaughn finds it Actually Pretty Funny.
- Take Our Word for It - Partway through the story, the Doctor says that it's time that they rescued Professor Watkins. The very next shot features one of Vaughn's men describing in detail the incredible, action-packed rescue operation that UNIT carried out, yet we never got the chance to see (it was scripted, but there wasn't enough time to film it).
- Ian Marter, who wrote the novelisation of the story, admitted that he was tempted to play the scene for laughs and reveal that all that had really happened was that the Doctor distracted Watkins' guard for a few moments while Benton rescued the professor, with the whole "rescue operation" being made up by the guard in the vain hope that Vaughn wouldn't execute him for his failure. In the end though, Marter kept the scene as it had originally been written.
- Twenty Minutes into the Future
- Uncanny Valley (In-Universe): The Doctor notices that Vaughn doesn't blink as often as a human should, a sign that he has a cyborg body.
- Utopia Justifies the Means - Unlike most Corrupt Corporate Executives, Vaughn believes in a greater good that justifies what he's doing.
- What Happened to the Mouse?: Whatever became of Rutledge?
- The novelisation has Vaughn ordering him to shoot himself. According to some sources, this was meant to happen in the TV version as well but...didn't.
- You're Insane!