[[caption-width-right:350: Not pictured: Horrifying noises courtesy of The Great Old Ones' grandfathers.]]
->''"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 one with the WesternAnimation/DaffyDuck Cyberman.

The TARDIS arrives in UsefulNotes/{{London}} in the near future, the Doctor and companions are enlisted by Isobel Watkins to find her uncle, 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, immobilizing 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, specifically the [[Creator/JonPertwee Third Doctor]]'s era, 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.

* AbsenteeActor: Zoe is absent from the third episode and Jamie only appears in a pre-filmed insert in the last, in order to give Wendy Padbury and Frazer Hines a holiday.
* 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.
* BeQuietNudge: The Doctor when Jamie keeps SayingTooMuch to Vaughn.
* BigBad: Tobias Vaughn.
* CallBack: There are numerous references back to the events of [[Recap/DoctorWhoS5E5TheWebOfFear The Web of Fear]] and many mentions of Professor Travers and his daughter Anne. When Lethbridge-Stewart first appears, the Doctor refers to him as "Colonel" before being corrected.
* CorruptCorporateExecutive: In keeping with the spy-thriller feel, Tobias Vaughn is very much a corporate [[Film/JamesBond Blofeld]].
* CutAndPasteEnvironments: The same set is used for Vaughn's office in two different buildings (with a different view out of the window). {{Lampshade|Hanging}}d.
* 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.
* TheDragon: Packer
* DrivingIntoATruck: The Doctor and Jamie are snatched off the street by two men driving an expensive car. Instead of being taken to the BigBad, they're driven to an airport runway and up the access ramp of a Hercules transport aircraft, where the Doctor meets his old ally Lethbridge-Stewart and the newly-formed United Nations Intelligence Taskforce.
* EarlyInstallmentWeirdness: The first time we see Benton he's [[TuxedoAndMartini wearing a suit and driving a Jaguar]], as there's more emphasis on UNIT being an international intelligence organization. After this UNIT is always presented as being strictly military.
* EvilIsNotAToy
* {{Expy}}[=/=]SuspiciouslySimilarSubstitute: Professor Watkins and his niece Isobel, the SuspiciouslySimilarSubstitutes written in when the actors of [[Recap/DoctorWhoS5E2TheAbominableSnowmen Professor Travers]] and his [[Recap/DoctorWhoS5E5TheWebOfFear daughter Anne]] were unavailable for filming. Professor Travers and Anne are [[PutOnABus said to have moved to America]], and Professor Watkins and Isobel fill their shoes ''extremely'' well. This is quite possibly {{lampshade|Hanging}}d by the fact that the Doctor and companions mention repeatedly that they were hoping to meet Travers and Anne before finding out that the pair are gone, even though they are otherwise unimportant to the story.
* FakeKillScare: A missile is fired at the Tardis, and the Doctor can't get the controls to work! Have our heroes been obliterated before their adventure even begins? Of course they haven't.
* ForInconveniencePressOne: Written in 1968, a rare example of ''Doctor Who'' predicting the future effectively.
* GettingCrapPastTheRadar: Vaughn isn't exactly clear on what Packer will do to Isobel or Zoe if they're turned over to him, but it's as strongly implied as it can be in ''Doctor Who'' that 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.
* KilroyWasHere: In Episode 3, scrawled on a wall in the elevator shaft. No real purpose, just set dressing.
* LargeHam:
** Viewers may remember Kevin Stoney from his former role as [[Recap/DoctorWhoS3E4TheDaleksMasterPlan Mavic Chen.]] His hamminess has seen no decrease whatsoever.
** Vaughn's assistant Packer also qualifies; he 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.
* MadEye: Vaughn's right eye is half-closed through most of the serial ([[RealLifeWritesThePlot due to injuries Kevin Stoney had suffered in a car accident]]), then opens wide when he turns against the Cybermen.
* 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.
* MeaningfulName: The United Nations ''Intelligence'' Taskforce implies the organisation was formed in direct response to "The Web of Fear", in case the Intelligence struck again. Of course it's also seen fulfilling a role as a UN spy organisation, at least in this episode.
* MegaCorp: International Electromatics.
* 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
* NoKillLikeOverkill: After the destruction of their invasion fleet, the Cyber Planner intends to destroy all life on Earth with a super bomb.
* NoodleIncident: The Cyber Planner tells Vaughn that he recognizes the Doctor and Jamie from Planet 14, an event we never saw.
* OffscreenMomentOfAwesome / 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).
* OutOfGenreExperience: This is a Troughton story that isn't a base-under-siege, features UNIT, a DiabolicalMastermind VillainWithGoodPublicity and Cybermen invading modern-day London, and feels like a test-run for the Pertwee era (because [[PoorlyDisguisedPilot it was]]).
* 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.
* PutOnABus: A BBC episode intro by the actor who plays Vaughn reveals that the roles of Watkins and his niece Isobel were originally written for [[Recap/DoctorWhoS5E2TheAbominableSnowmen Professor Travers]] and his [[Recap/DoctorWhoS5E5TheWebOfFear daughter, Anne]]--but the actors weren't available at the time of filming, so Professor Travers and Anne are said to have moved to America, and [[SuspiciouslySimilarSubstitute Professor Watkins and Isobel]] fill their shoes.
* RankUp: Colonel Lethbridge-Stewart is now TheBrigadier.
* RedRightHand: Tobias Vaughn has a heavy squint and, as the Doctor observes, barely ever blinks.
* RedemptionEqualsDeath: Vaughn. Well, sort of, since he claims he just wants revenge.
* SeriesContinuityError: The animated first episode depicts Zoe wearing the clothes that she later gets from Isobel when she should be still wearing her glittery catsuit from "[[Recap/DoctorWhoS6E2TheMindRobber The Mind Robber]]". This may have been an error or may have been due to a desire not to have to create a second character model.
* ShoutOut:
** In the animated first episode, the car that the Doctor, Jamie, and Zoe hitch a ride with after the lorry driver is shot has the license plate H 23 63, which is a reference to the date of the original broadcast of "[[Recap/DoctorWhoS1E1AnUnearthlyChild An Unearthly Child]]", the very first episode of ''Doctor Who'', on 23 November 1963.
** In the same episode, the words "Bad Wolf" (the story arc of the 2005 series) are written on Isobel's wall as an in-joke.
* SpoilerTitle: Unusually for Classic ''Who'', averted. A BBC episode intro by the actor who played Vaughn reveals that the serial was originally going to be titled "Invasion of the Cybermen", but was shortened to avoid spoiling the Cybermen, who don't appear until halfway through the 8-episode serial.
* StayInTheKitchen: Isobel learns her lesson against feminist assertiveness after she gets a RedShirt killed.
* TheStarscream: Tobias Vaughn is working with the Cybermen to invade the planet, but plans to betray them and rule the world. He ends up helping to defeat the Cybermen but is killed by them.
* StockEpisodeTitles: 40 uses.
* StockFootage: The exact same footage of missiles pivoting up, then cutting to the behind view, then a single missile rotating across a clear sky, is used three times in three successive episodes. This wouldn't have been so obvious to the audience watching it week-by-week, but is painful in an ArchiveBinge (it doesn't help that at least two are EngagingChevrons sequences).
* SurroundedByIdiots: Vaughn has his incompetent henchman Packer -- unusual given his stated desire for efficiency.
* SuspiciouslySimilarSubstitute: Professor Watkins for Professor Travers and Isobel Watkins for Ann Travers.
* TakeOverTheWorld: This is Vaughn's ultimate goal. Much like Klieg in "[[Recap/DoctorWhoS5E1TheTombOfTheCybermen The Tomb of the Cybermen]]", he goes on a rant about how the world is a disorganized mess of conflicting ideals, and only his superior intellect could bring it together to solve all its problems.
* TalkingTheMonsterToDeath: Zoe talks IE's computer receptionist to death with a LogicBomb. Vaughn finds it ActuallyPrettyFunny.
* TwentyMinutesIntoTheFuture: Takes place 4 years after "[[Recap/DoctorWhoS5E5TheWebOfFear The Web of Fear]]" which would theoretically put it in the very early 70s. (See that article for more, and for the beginnings of the infamous "UNIT Dating Controversy".)
* 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. He allies with and manipulates the Cybermen into taking over the world for him, so he can then doublecross them and create a utopia where all ideological disputes cease and unity is attained. Unfortunately for Vaughn, the Cybermen were one step ahead and doublecrossed him first, leading him to [[EnemyMine ally with the Doctor]] to take down the threat that he himself had led to the Earth in the first place.
* VillainousBreakdown: Tobias Vaughn goes from his usual cold and calculating personality to launching a raging freak out at an underling (and once, to the Doctor) in every single episode of the story that he's in.
* WhamLine: The Doctor to Tobias Vaughn at the end of Episode Seven (and, by extension, the beginning of Episode Eight):
-->'''The Doctor:''' Is this what you wanted, Vaughn?! To be the ruler of a ''dead'' world?!?!
* WhatHappenedToTheMouse: Whatever became of Rutledge?
* WholePlotReference: The plot is similar to ''Series/QuatermassII'', though not as much as some other stories.
* WhoWouldBeStupidEnough: Vaughn lets loose the deranged Cyberman into the sewers, saying that anyone stupid enough to be roaming around in a sewer [[KickTheDog deserves anything that happens to them]]. AnswerCut to Isobel who's planning to do exactly that.
* WrittenInAbsence: Jamie and Zoe each miss an episode, due to their actors being on holiday. The in-story reasons are that Jamie was in hospital after being injured, and Zoe was imprisoned by Vaughn after blowing up his computer receptionist.
* YearOutsideHourInside: It's been four years since Lethbridge-Stewart last encountered the Doctor, but to Jamie and the Doctor it's only been a few weeks due to their time traveling.
* YouHaveFailedMe: Bye-Bye, Gregory.
* YouHaveOutlivedYourUsefulness: Both Vaughn and the Cybermen are planning to do this to each other, but the Cybermen end up getting the jump on Vaughn.
* YoureInsane: Professor Watkins says this to Vaughn about his plans.