If The Brain of Morbius felt like the companion piece to Pyramids of Mars, this makes a neat pair with Terror of the Zygons: same writer, director, composer and contemporary Earth setting. It recaptures the slightly eerie quality of the earlier story, the sense of the uncanny intruding into the real world, taking its time to establish its characters without over-burdening the audience with too much plot. Broadly, this all works so effectively B-movie lines like, ‘It’s as if he’s turning into some sort of a hideous monster’ just wash over us.

Tom Baker’s performance helps: by some accounts he was dismissive of the material. If that’s so, it comes across on screen as grim determination to get to the root of the Krynoid incursion, and try to prevent a disaster. He’s quite po-faced when confronted with the infected Winlett, and coldly dismisses Moberley’s appeals for his medical intervention: ‘You must help yourselves.’ It takes Sarah Jane to step in and talk Moberley out of his squeamishness in the closest the classic era comes to ‘She cares so I don’t have to.’ I like how he takes Sarah’s questions quite seriously, considering how the Krynoid pods came to be on Earth and admitting he doesn’t know but has some theories.

With a waking evil buried for 200 centuries, a human body being consumed by something alien (Winlett’s single, staring eye is very like Noah’s), and human greed placing everyone in terrible danger this has all the hallmarks of another Holmes and Hinchcliffe classic.

Next episode: The Seeds of Doom – Part Two