[Spoilers]

It’s obvious that Dask is the killer from the start of the episode – at least, the Doctor heavily hints he is, suggesting he knows exactly where to look for the damage that’s crippled the Sandminer, and that, ‘I think he’s very clever.’ Which means anyone in the audience paying attention has worked it out before the end of the first scene, and the moment when we see a barely-obscured image of Dask on the monitor doesn’t actually blow anything. I suppose keeping Uvanov off stage until the end of the episode also casts suspicion on him, but the clues all point to Dask. In fact, this is beautifully structured so that anyone invested in the story can piece together exactly whodunit and why, and anyone who’s just half-watching can enjoy some witty moments (the robots’ deadpan, polite advice that they want to kill you), some genuinely creepy visuals (the based-in head of a Voc, and its hand dripping with blood), and brilliant performances.

Boucher’s script also lightly but effectively develops the characters. Poul is faintly dismissive of his comrades on the Sandminer, and their lust for money; his aversion to robots (‘I’d rather live with people’) foreshadowing his nervous breakdown when he realises the Doctor was right and the robots, or the ‘walking dead’ as he calls them, are bumping people off. But before he loses his mind he tells Leela Uvanov’s dirty secret: he sacrificed Zilda’s brother in pursuit of a rich vein of lucanol (presumably named after the elusive Lord Lucan). This is all brilliantly pastiching detective thrillers, as is the Doctor’s suggestion that everyone should gather on the bridge.

Curiously, given it’s written by her creator, the only moment that jars for me is Leela’s ‘Now you’re showing off’ to a murderous robot, which doesn’t quite sound like something Leela would say. Everything else about this works. Like the best Doctor Who, it wears its influences lightly, and transcends the material it borrows from by juxtaposing and mixing genres: Golden Age Crime and Golden Age Sci-Fi, but crucially doing a very convincing take on both.

Next episode: The Robots of Death – Part Four