Written by Terrance Dicks, based on Bob Baker and Dave Martin’s scripts for the 1977 TV serial.

The third Baker and Martin adaptation in a row. It’s less gruesomely sadistic than Doctor Who and the Sontaran Experiment, but a bit brisker and more amusing than Doctor Who and the Hand of Fear, with Dicks picking out the comic moments in the scripts and inserting a few jokes of his own (such as the “Germanic” Professor Marius having studied at “New Heidelberg University, Marius had come to the asteroid belt in search of new and rare diseases. So far he had come up with nothing sufficiently exotic to satisfy him.”)

Dicks does his usual tarting up of the less effective onscreen effects. The derided Nucleus of the Swarm becomes an almost Lovecraftian horror, “waving antennae, glistening wet red flesh, and a bulbous black eye that seemed to swivel to and fro”. The swarm itself is made up of giant dragonfly creatures. However, Dicks knows when to stay true to the programme as broadcast, and K9 in his introduction is “a squat metallic creature that stood near the bottom of the bed. It looked curiously like a kind of squared-off metal dog, with a computer display screen for eyes, and antennae for ears and tail” and not the larger robot described in the scripts.

Separated from its shoddy production, The Invisible Enemy is revealed as a rather more effective story than was realised, with the Doctor’s possession leading to some quite tense moments as he battles to stop himself from killing the “reject” Leela. I liked the vague implication that Leela’s immunity might be a paradox, as the 51st Century is said to be the time of her ancestors – maybe the immunity she provides them will find its way down through the generations. Not a standout, but a solid Dicks effort. Grade 3.

Next Time: Doctor Who And… The Robots of Death.