A procedural episode that continues the holding pattern from the last week, albeit with a trip into the medical centre for a change of scenery where the Doctor discovers more sinister duplicates and alien equipment; he continues to wind up the indignant Commandant, and throws out more wild theories about what the Chameleons are doing.  Hulke and Ellis throw in a few other flourishes like the Goldfinger style laser cutter – to add a few minutes of jeopardy to pass the time, but this is very much a bog-standard capture/escape middle episode.

While there’s not a great deal of new material, the characterisation at least remains strong, even for the supporting characters. Wanda Ventham as the droll Jean Rock gets to fake a fainting fit to help the Doctor distract the fierce Nurse Pinto, and the converted Jenkins is given a plausibly mundane backstory: he lives with his parents (surprise surprise) in Wimbledon. And Sam Briggs continues to be excellent value as she takes the initiative and books herself on a Chameleon Tour. ‘A lot of courage, that wee lass,’ says Jamie, admiringly. ‘A very strong-headed young woman,’ concurs a less enamoured Doctor.

While it’s not the most shocking twist in the world considering we know they’re aliens, the cliffhanger – the Chameleon aircraft’s wings folding back as it heads vertically into orbit to rendezvous with a huge spacecraft – is pretty spectacular. It’s also very modish given this aired about six weeks before the premiere of You Only Live Twice, which features a spacecraft that similarly swallows up smaller vehicles. Combined with the Goldfinger reference, the sense is Hulke and Ellis using the script to work out their Bond movie ideas.

Next episode: The Faceless Ones – Episode 5