“I am a soldier.” “You’re not a soldier, you’re a doctor.” “I am an army doctor, which means I can break every bone in your body, while naming them.” Oh I’ve missed their squabbles. And I’ve enjoyed this one, much more than I did the end of the previous season. It got some of the proper spirit back, and lots of mind palaces and riddled stories.

The Victorian framing device is the episode's genuine achievement — Moffat and Gatiss at their most formally playful, using the period setting to interrogate the mythology the modern series had built. Cumberbatch and Freeman are clearly energised by the costume-change. The nested-narrative structure is clever without being quite as clever as it thinks; the final act resolves the frame too neatly. A confident formal experiment that works better as a one-off than as a series entry.

Incomprehensible as a standalone movie, pretty good as a special episode. I still wish they gave up on casting M every chance they get, but I guess I’m the only person in the world to dislike him.