[[quoteright:350:http://static.tvtropes.org/pmwiki/pub/images/_41631822_invasion1_416bbc_5135.jpg]]
[[caption-width-right:350: Not pictured: Horrifiying noise by courtesy of The Great Old Ones' grandfathers.]]
->''"You're an evil man, Vaughn. You're sadistic. You're a megalomaniac. [[YoureInsane 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 UsefulNotes/{{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 "[[Recap/DoctorWhoS5E5TheWebOfFear 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.


!!Tropes

* AffablyEvil: Tobias Vaughn. Very courteous, even to trespassers, as long as one is not hindering his plans. [[LargeHam But when he gets upset...]]
* AnimatedAdaptation: The two missing episodes were remade in an animated format for the DVD release.
* CallBack: There are numerous references back to the events of "The Web of Fear" and many mentions of Professor Travers and his daughter Ann. When Lethbridge-Stewart first appears, the Doctor refers to him as "Colonel" before being corrected.
* CorruptCorporateExecutive
* CutAndPasteEnvironments: The same set is used for Vaughn's office in two different buildings (with a different view out of the window). {{Lampshaded}}.
* CyberneticsEatYourSoul: 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.
* EvilIsNotAToy
* {{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 "[[Recap/DoctorWhoS6E1TheDominators The Dominators]]" and the IP ownership of the Quarks.
* ForInconveniencePressOne: Written in 1969, a rare example of ''Doctor Who'' predicting the future effectively.
* GenreSavvy: 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. He out and out tells Packer that he knows the Cybermen will try to take over once the invasion has occurred, but that he's planned for everything.
* GettingCrapPastTheRadar: 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.
* IdiotBall: 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.
* ImmuneToBullets: Vaughn, thanks to voluntary partial Cyber-conversion.
* KidnappedScientist: Professor Watkins.
* LargeHam: Viewers may remember Kevin Stoney from his former role as [[Recap/DoctorWhoS3E4TheDaleksMasterPlan Mavic Chen.]] His hamminess has seen no decrease whatsoever.
** Not to mention Vaughn's assistant Packer, who takes so much pleasure in his actions that he constantly looks like he's holding back a snicker.
* LogicBomb: Zoe uses ALGOL to blow up the computer receptionist.
* MagicSkirt: Well, kilt - the girls' skirts [[PantyShot definitely don't do this]], but Jamie's kilt stays in place. It's not magic, though - it's weighted.
* ModestyShorts: 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 [[PantyShot had other ideas]].
* MultinationalTeam: UNIT
* PantyShot: 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.
** Rather humorously, the animation team for the missing episodes on DVD actually removed Isobel's ModestyShorts in the scenes where she's climbing up the ladder.
* RankUp: Colonel Lethbridge-Stewart is now TheBrigadier.
* RedemptionEqualsDeath - Vaughn. Well, sort of, since he claims he just wants revenge.
* StockEpisodeTitles: 40 uses
* SurroundedByIdiots: Vaughn has his incompetent henchman Packer -- unusual given his stated desire for efficiency.
* [[TalkingTheMonsterToDeath Talking The Computer To Death]]: Zoe! Vaughn finds it ActuallyPrettyFunny.
* TakeOurWordForIt - 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.
* TwentyMinutesIntoTheFuture
* UncannyValley (InUniverse): The Doctor notices that Vaughn doesn't blink as often as a human should, a sign that he has a cyborg body.
* UtopiaJustifiesTheMeans - Unlike most [[CorruptCorporateExecutive Corrupt Corporate Executives]], Vaughn believes in a greater good that justifies what he's doing.
* WhatHappenedToTheMouse: 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.
* YoureInsane
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