"This is the most difficult case in my career", says Poirot at one point. "I'm trying to solve a crime that does not exist".
When Poirot meets the son of an old friend of his, a writer who is engaged to a beautiful fashion model, he senses that something might be wrong. The model's previous boyfriend, a sculptor, still seems to be in love with her. A sinister-looking old man is constantly lurking about. And why does this nest of wasps at the writer's garden seem to be so difficult to exterminate?
Sometimes it's hard to explain why a film, or a TV episode in this case, works so well, you just have to experience it for yourself. The story itself is ingenious (this time, Poirot has to connect the pieces to prevent a future crime, not solve a past one), and the ending left me speechless. But what gives "Wasps' Nest" an extra layer is how unexpectedly moving and quiet its resolution is. Up to this point in the series (Season 3, Episode 5), this is a candidate for best episode. (***1/2)