How Does Your Garden Grow?

Poirot meets a woman in a wheelchair at the Chelsea Flower Show. She hands him an empty seed packet, which is not the sort of thing one usually receives from a stranger among the blooms, and asks him to call on her the next day. He does. She is dead, poisoned, and the seed packet is about all he has to go on. It is the kind of meeting that would be forgettable, except that Poirot does not forget anything.

It is a lovely opening, and the episode keeps the promise. The investigation spreads out from the dead woman, Amelia Barrowby (Margery Mason), into the lives of the people around her: Mary Delafontaine (Anne Stallybrass) and her husband Henry (Tim Wylton), the companion Katrina Reiger (Catherine Russell), Nicholai (Peter Birch), Dr Sims (Ralph Nossek). Hastings comes along for the walk. Japp makes the official noises, and Miss Lemon does her quiet work. And somewhere in the middle of it all is the garden itself, which turns out to matter more than anyone first thinks.

Andrew Marshall wrote the script with Agatha Christie, and Brian Farnham directed. It is a poison case with a slow, patient build, the kind that rewards attention. Margery Mason makes Amelia worth caring about in a single scene, which is no small thing for a woman who gets no chance to speak after that first meeting.

There is a particular satisfaction in a mystery that starts from something as small as an empty seed packet. The whole story grows out of it, which is a trick Christie used more than once, and it works beautifully here. The title asks the question, and the episode answers it in a way that has nothing to do with horticulture. Watch it twice. The second time, you can see the seeds being planted.