The first part of this episode is genuine base under siege stuff, with strong Night of the Living Dead overtones as the Doctor, Sarah, Scorby and some toughs spend the night in a cottage while the Krynoid prowls outside, and tensions grow between the survivors. It’s tense: Baker practically spits half his dialogue, but I think it’s a bit of a shame they jumped the gun and gave the Krynoid a voice. Its bargain with Scorby for the Doctor’s life doesn’t go anywhere, and it would have been better to have it as a horrible, unknowable presence in the darkness rather than a standard Doctor Who whispering villain.

Far better to have waited until Chase falls under its spell, and becomes its mouthpiece (or, just perhaps, he’s gone insane and this is his own interpretation of the Krynoid’s natural urge to live and reproduce). Tony Beckley’s performance is one of the highlights of the serial: constantly on the edge of madness, here he tips right over, believing himself to be the chosen one of the Krynoid, and swearing death to all animalkind. The cliffhanger is, brilliantly and much more chillingly, not a shot of the now-giant Krynoid menacing the Doctor and co. locked out of the mansion, but of Chase’s smiling face as he listens to their desperate screams.

Very weirdly, and working against the base under siege aspects of the script, this also features a detour for the Doctor who – implausibly – abandons Sarah Jane to drive to London for a conference with Sir Colin and Major Beresford of UNIT (the Brigadier, as usual, is in Geneva) where they all joke about killer gooseberries. I don’t like this at all: it’s not as if UNIT are a major presence in the story (aside from Beresford they’re represented here by a sole sergeant) and I don’t buy the Doctor driving for miles while Sarah is left with the dangerous Scorby (who’s already tried to kill her and doesn’t seem far off sacrificing anyone to save his own skin), the insane and murderous Chase, and the growing Krynoid. An easy tweak would have been to reverse their roles, and have Sarah Jane travel to Sir Colin while the Doctor remained. As it stands, I don’t think this quite works and, alongside the Doctor carrying a gun, is representative of a story that doesn’t sit entirely comfortably.

Next episode: The Seeds of Doom – Part Six