The Invisible Enemy was my least favourite Fourth Doctor Doctor Who serial but last night, watching it again, I warmed up to it quite a bit. Looking for Doctor Who stories about a virus epidemic, it's the first one that comes to mind--an intelligent virus takes over the crew of a base on Titan, turning people into their slaves with furry, scaly eyes.
The Doctor (Tom Baker) and Leela (Louise Jameson) are bantering on the TARDIS when the virus somehow transmits to the TARDIS console and implants the "Nucleus", the virus leader, into the Doctor's brain. It doesn't manage to take him over fully until he and Leela arrive on the Titan Base.
I remember hearing how people working on the show, and I think Baker himself, were reluctant to show the Doctor himself doing anything nasty, even if it was a clone of the Doctor or the Doctor possessed, and this led to a modification of a scene in a later serial, The Stones of Blood, in which the Doctor seemed to be attacking Romana. In The Invisible Enemy, the first episode ends on the Doctor pointing a gun at Leela from behind. The tip-off that he's possessed is that his hand is covered with white fur and scales.
It quite reminded me of David Cronenberg's Videodrome when James Woods' character becomes a thrall assassin for a sinister organisation transmitted over television waves. Woods' hand holding a gun similarly undergoes a transformation. The Doctor more successfully fights off the virus in the beginning of Part II but I got to wondering if maybe the episode was meant to be more of a political allegory that was altered on the spot. Still, the story is about a virus trying to take over human civilisation.
I'm not alone in thinking it's the weakest Fourth Doctor serial--the Wikipedia entry quotes only negative reviews for it, from the time it aired and from recent retrospectives. I suppose the main problem is that, while there are clear thematic ideas, the story delivers them a bit clumsily. Perhaps because my expectations were lower, I was appreciating them on the terms of dream logic last night. When the Doctor goes into a trance, then has himself and Leela cloned and miniaturised and sent into his own brain--and the clones seem to have no problem with their projected eleven minute life span (though no-one mentions they manage to last through two episodes)--there's so many leaps in logic the only way to appreciate it is to let go. When the Doctor clone, inside the Doctor's brain, tells the Leela clone that a tiny bridge across a pitch dark space is the gap between the brain and the mind, intelligence and creativity, the correct response is, "Yeah, man, I dig, far out."
It's not hard to see which side of the chasm The Invisible Enemy is on. I suppose it's fitting for the serial that introduces K-9.