15x2. The Invisible Enemy
Writers: Bob Baker and Dave Martin
Director: Derrick Goodwin
Script Editor: Robert Holmes
Producer: Graham Williams

Synopsis: The Doctor is infected by a virus that has the ability to take over someone's mind and is using infected humans to create a dangerous "swarm." Leela, who is immune to its effects, helps fight the virus as the Doctor struggles to resist it and the two of them end up under siege at a space station near Titan. After defeating the virus, the Doctor and Leela gain a new companion: an intelligent robotic dog named K-9.

Review: "The Invisible Enemy" is a passably entertaining installment of Doctor Who (some fans apparently absolutely hate it, but I'm not among their number); however, it has enough minor flaws and odd storytelling choices that it doesn't earn a full recommendation from me. For example, the Doctor has a theory that Leela is immune to the virus because it's seeking strong intellects and she operates mostly on instinct -- first of all, my impression has been largely that Leela is not unintelligent but simply uneducated, and this seems a bit inconsistent. And second of all, the Doctor later identifies some sort of "fishhook"-shaped substance or organ as a critical difference between his brain and Leela's -- is this meant to discredit his earlier theory, or is the presence of this component the cause of their differences in intellect and temperament? And while the Fantastic Voyage-style journey through the Doctor's brain is an interesting storytelling device (particularly when it leads to some amusing banter between the Doctor and Leela), the "cloning" technology that enables it is so ridiculous -- it replicates all past memories and even clothing, apparently -- as to defy even suspension of disbelief. On the positive side, the Doctor's struggle to resist the virus gives Tom Baker the chance to play up the character's alien nature (such as when he completely "withdraws into himself" rather than risking staying conscious), something he always does well. And there is something of an interesting theme here regarding humanity's history of conquest -- Leela refers to her ancestors as "new frontiersmen" from Earth, and the viral nucleus lodged in the Doctor's brain argues for its own right to survive. The Doctor would seemingly agree if the swarm's goal wasn't a conquest of their own, and he tries (though he ultimately fails) to find a solution other than simply blowing up the Titan base where the viral incubation procedure has begun. But this also highlights the extent to which this is something of an inferior "Ark in Space" retread, and "The Invisible Enemy" doesn't bring anything to this conflict that we haven't seen on Doctor Who before.

Rating: **1/2 (out of four)