The title of the Doctor Who episode “The Invasion” hints at what the story would be about, but it keeps the viewer in suspense – although with some big hints – before eventually revealing who or what would be doing the invading. Since the cover of the DVD case doesn’t keep the secret, presumably it won’t be considered a spoiler that I didn’t either.
This episode, like a number of others during the Patrick Troughton era, had a strong element of mystery, intrigue and espionage.
It also saw the return of Alistair Gordon Lethbridge-Stewart, now at the rank of brigadier, the title which has remained the most common way of referring to the character ever since. Here he is associated with UNIT, the United Nations Intelligence Taskforce, which has also featured on the show regularly ever since it was first introduced in this episode.
As with all episodes featuring the cybermen, the value of human beings with their full range of frailties and emotions is explored. Here the spectrum of possibilities is wider, accomplished through the inclusion of a human being with a cybernetic body but an unaltered human brain. The fact that we regard replacement of some or all of body parts as not fundamentally altering us, while most consider it to be the case that removing emotion or otherwise altering the brain would fundamentally change us, indicates what may be obvious to many but is nonetheless worth saying: we consider what makes us human to have to do with our brains – and the consciousness and emotional life centered in our brains – than with any other part of the body.
Any discussion of the nature of human beings – with or without reference to the “soul” – intersects with religion. In the episode Jamie makes the connection explicit, as he asks, after the Doctor notices that Tobias Vaughn (whom we later learn has a cybernetic body) blinks less frequently than humans normally do, whether he had a pitchfork and forked tail.
The ambiguous view of the appropriateness or otherwise of skepticism in science fiction also appears, as UFOs are mentioned (in fact spacecraft of the Cybermen, not saucer-shaped) and as there is a quest to obtain photographic evidence to not seem crazy when telling UNIT HQ in Geneva about the Cybermen.