Wasps' Nest

Poirot arrives with a feeling he cannot quite shake: a murder is being planned, and he believes he knows the target. The danger centres on the son of an old friend, John Harrison (Martin Turner), and his girlfriend Molly Deane (Melanie Jessop), a fashion model who looks as though she has wandered in from a glossier world. But nothing has happened yet. That is the point. Poirot is trying to stop a crime before it starts, which is a different kind of work from solving one.

He brings Hastings along, and here the episode plays a neat card. Hastings has taken up a new hobby, and it turns out to be exactly the tool the case needs. The surrounding village supplies the usual suspects and bystanders: Claude Langton (Peter Capaldi, well before Doctor Who, showing the quiet menace he would later put to other uses), Dr Belvedere (John Boswall), Mrs Henderson (Kate Lynn Evans), and a Model Girl (Serena Scott Thomas) who may not be as peripheral as she looks. Molly Deane is played by Melanie Jessop with the right kind of brittle confidence. Japp and Miss Lemon put in their customary appearances.

David Renwick wrote the script with Agatha Christie, and Brian Farnham directed. It is a short, sharp story, more about prevention than detection, and it moves at a good clip. It is an unusual structure for the series, and the change of pace suits the story.

The title does its work. You do not wave at a wasps' nest; you deal with it carefully, or you get stung. Poirot is very careful here, and the episode respects that. There is no body to find and no crime scene to measure, just a plot that needs dismantling before it can work. The story stays with you longer than its running time suggests, which is about the best thing you can say for a short mystery.