This is almost as scattergun as Terror of the Autons: we’re presented with UNIT observing a revolutionary new method of rehabilitating criminals; investigating a World Peace Conference threatened by allegations of international espionage, and transporting a missile. Last time Don Houghton wasn’t sure if his story could stretch to seven episodes he chucked in a parallel universe plot which added an extra element of tension to Inferno. This time, it just feels like a string of unfortunate coincidences.

Of course, these events are connected as this episode starts to make clear: the mysterious Emil Keller has a ‘rather attractive Chinese girl’ assistant (echoing Captain Yates’ unlikely description of Chin Lee as ‘quite a dolly’). It very much has that vibe of a late 1960s/early 1970s Christopher Wicking sci-fi thriller made up of various fragmented concepts (something like Scream and Scream Again, a style Houghton adopted for The Satanic Rites of Dracula). It’s a bewildering mix of fairly “gritty” scenes, like Chin Lee burning stolen papers in a children’s playground like she’s in a spy film, and weird, pulsing audio-visual electronic effects as Kettering is drowned in a dry room (the Keller Machine apparently able to physically as well as mentally affect its victims, including magicking up some water).

The Machine itself – apparently the first of the plots Houghton came up with (and the fact that it’s the one the Doctor is investigating clearly signals it’s key) – is a great idea (basically the same concept turns up with Brad Dourif in a 1990s Babylon 5 episode), and the way it’s presented as a sort of electric chair, with the condemned man led through a riot of prisoners banging on their bars to his doom, gives it an added ominousness. Plus, in between the Machine’s attacks it’s shown to actually do what it’s meant to – turning a hardened criminal into a gentle person.

Nevertheless, the Doctor’s instant antipathy towards the entire process is telling. Possibly this is just his aversion to the execution of justice given his own experience at the hands of the Time Lords, but, just like in The War Machines and Inferno, the Doctor seems to have a sixth sense when there is evil afoot. And again, his demands to destroy the machine are met with baffled “above my pay grade” obfuscation from the local civil servant.

After being quite grumpy in the previous serial, Pertwee seems to be enjoying himself much more in this, behaving like a naughty schoolboy when he’s talking with Jo (waving at the camera at the prison gates, or providing a sarcastic commentary during the Keller Machine test). And his new red jacket stands out brilliantly among the dark suits of the other attendees. 

Next episode: The Mind of Evil – Episode Two