S02E03 - The Cornish Mystery

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. There could be no financial motive to suggest why Mr. Pengelley should try to murder his wife but she suspects an affair with his young receptionist. Another resident in the house was her niece, Freda Stanton, but that lady rowed with Mrs. Pengelley the week before and left the house after living there for eight years. Mrs. Pengelley is vague as to the cause of the row but states that she has been told by a Mr. Radnor to leave Freda to come to her senses. Radnor is described as "just a friend" and a "very pleasant young fellow".
Poirot and Hastings travel to Cornwall the next day and are shocked to find that Mrs. Pengelley died half an hour before. The maid who answers the door makes it clear that she too suspects the husband. Poirot interviews Mrs. Pengelley's doctor who at first denies that anything could be wrong but is then astounded to hear that the dead woman came to London to consult the detective.