The Cornish Mystery — Agatha Christie

Poirot receives a visit from a Mrs Pengelley, a middle-aged woman who is afraid that she is being poisoned by her husband, a dentist. She has been ill after eating but her doctor states that she is suffering from acute gastritis. She and her husband live in Polgarwith, a small market town in Cornwall. She has no proof of the allegation, only that she only suffers when her husband is at home, not when he is away at the weekends and a bottle of weedkiller, supposedly unused, is half-empty!