‘Sometimes the only choices you have are bad ones, but you still have to choose.’ This plays like the other half of a diptych, picking off where Kill the Moon left off, with Clara sticking to her guns about leaving the TARDIS, but consenting to one last trip to avoid parting on bad terms. Inevitably, it’s a trip that ends in chaos and destruction with an invisible mummy taking 66 seconds to hunt down and kill each victim, and an equally invisible mastermind hoping to nefariously harness its powers.

I enjoy how, like the Agatha Christie novel that inspired the title, Jamie Mathieson’s script has a single-mindedness to it as it focuses on the mummy’s inexorable advance (indicated by the 66-second countdown that appears each time it begins to hunt). The creature itself is memorably grotesque – like the Weeping Angels, it has a unique method of stalking its prey, but it’s even more terrifying because there’s no way to stop it once it turns its mind to you. As in the Christie novel, the main characters are all on board the Orient Express for a reason, and it’s understanding what connects them, plus the one scrap of physical evidence, that points towards the solution.

The only sub-plot is Clara’s dawning realisation that, despite the Moon, she can’t walk away from the Doctor. The impossible girl loves making the impossible choice: ‘You can’t really tell if something’s an addiction till you try and give it up.’ Even here, when he makes her his accomplice in a lie, she can’t stick to her guns. Instead, it’s Danny she repeatedly lies to (when he demanded she shouldn’t). There’s a definite sense that this toxic menage a trois can’t be leading anywhere good.

I think this is a pretty great episode, easily the best Capaldi so far. The Doctor is still doing the heartless act, but here it’s clear that it is an act, and it’s his impetuous heroism that rightly saves the day. He even offers Perkins the chance to join his crew. There’s a starry cast, as befits an Agatha Christie spoof. My complaints are firstly that having the real villain get away scot-free isn’t in keeping with Christie (or Doctor Who, generally), and secondly that Monster on the Orient Express sounds better than Mummy.

Next Time: Flatline