The Agatha Christie allusions continue to be obvious: the scenes of Poul telling Uvanov, ‘We’ve all got something to hide’, and Zilda discovering something incriminating in Uvanov’s quarters just before she’s strangled are pure murder mystery. But again, this is all surface gloss. The real story Boucher wants to tell is quite hard SF: in a civilisation that has become dependent on robots, but failed to escape the uncanny valley (Uvanov’s ‘tin brains’ insult nods to the idea that these people aren’t as comfortable with the robots as they pretend), the revelation that the First Law of Robotics can be bypassed is liable to cause society to collapse.

I feel this is the kind of story Christopher Bidmead aspired to in Season 18, but never quite managed to balance the SF ideas with its effortlessly accessible execution. Here, everything just works. Michael E Briant’s direction isn’t overly showy, but there are some neat touches – like the inset of the robots in the vast hangar bay – that sell the scale of the Sandminer and the SF setting, whiile D84’s POV shot and the guarded glimpses of the corpses are spins on standard murder mystery cinematography.

The performances are generally as strong as the material, although there are one or two weaker moments mainly involving Zilda. David Collings is especially impressive, particularly his panicked eyes when the Doctor plants the horrible idea that the robots are murdering the crew. For the second time this season (after The Deadly Assassin), the second episode of a serial sees the Doctor joining forces with a local investigator. It’s even more effective because for the most part the clues are more relatable than staser bolts and biog data extracts. And Louise Jameson continues to be great as well, although Leela seems to have acclimatised very quickly to time travel, spinning round in a chair, and dropping out of character to say, ‘thank you’ in a posh voice when she’s released from her restraints.

Next episode: The Robots of Death – Part Three