The Adventure of the Cheap Flat

Somebody has stolen the United States Navy's plans for a new submarine, and the trail leads to London. That brings in the FBI, which brings in Chief Inspector Japp, which brings in Poirot, because these international tangles have a habit of ending up in his sitting room sooner or later. The FBI sends an agent to work with Japp, and the search for the blueprints begins in earnest.

The hunt takes Poirot through a London full of people who seem to matter only at the edges: Stella Robinson (Samantha Bond, a future Miss Moneypenny, which is the sort of casting coincidence the show enjoys) and her husband James (John Michie), Elsie (Jemma Churchill), Mr Paul (Peter Howell), Carla Romero (Jenifer Landor), Teddy Parker (Ian Price). Each one carries a piece of the answer without knowing it, which is the classic arrangement. Hastings follows along gamely, and Miss Lemon keeps Scotland Yard's paperwork in some kind of order while the men chase the plans.

Russell Murray wrote the script with Agatha Christie, and Richard Spence directed. It is a brisk, well-stocked hour: espionage on paper and small human motives underneath, with Poirot doing what he does best, which is noticing what everyone else has decided not to. The ensemble is well served, John Michie and Samantha Bond making the Robinsons a couple worth watching, and Jenifer Landor's Carla Romero lingering in the memory.

There is something cosy about watching a matter of international security shrink down to a handful of London rooms and the people in them. The stakes are high and the canvas is small, and that mismatch is the appeal. The plans are recovered, the agent goes home satisfied, and Poirot returns to his quiet rooms. And the episode is the kind that rewards a second viewing, once you know who is telling the truth and who is simply telling a story.