The Invisible Enemy is the second serial of the 15th season of the British science fiction television series Doctor Who, which was first broadcast in four weekly parts on BBC1 from 1 to 22 October 1977.
In the serial, an intelligent virus intends to spread across the universe after finding a suitable spawning location on the moon Titan.
The crews of both ships are infected by a sentient virus, which chooses The Doctor to be the host of its "mind," the Nucleus of the Swarm.
The Doctor manages to break free of his infection and tells Leela how to get the TARDIS to the nearest medical centre.
[5] Reviewing the serial for The Times newspaper on the Monday following the second episode's transmission, critic Stanley Reynolds gave the story a generally negative reception.
He also pointed out that in ITV regions where the series was competing with Man from Atlantis in the Saturday early-evening slot, it was now losing the ratings war: In the current story, The Invisible Enemy, now halfway through its four-week run, a malignant virus has struck a space station.
When one is being 'taken over' those sort of lightning flashes like the advert for learning how to hypnotise, travel from the eyes of the villain to the one having the fluence put upon him.
Paul Cornell, Martin Day and Keith Topping wrote of the serial in The Discontinuity Guide (1995), "An ambitious project which has the look of a grand folly due to budget constraints and the tongue-in-cheek script... K9 makes a quite impressive debut, though, as with many aspects of The Invisible Enemy, the ideas are better than the realisation.
"[7] In The Television Companion (1998), David J. Howe and Stephen James Walker called it one of the "weakest" Fourth Doctor stories, mostly consisting of "clichéd and undemanding action-adventure material".
He praised the story as a "romping yarn" which "brings out the best in veteran designer Barry Newbery", but criticised "unbelievably incompetent" action scenes, as well as "harsh lighting" and "pristine white sets".