Miss Marple is convinced that the death of the schoolgirl Pamela Reeve holds the key to the mystery of the double murder. There are a number of suspects, but the police finally arrest Basil Blake. Miss Marple, however, draws an entirely different conclusion. After a train journey to London, she comes back with evidence that allows the police to stage a trap for the real killer.

The ordered tranquility of life in St Mary Mead is shattered by a mysterious discovery. Miss Marple's investigations lead her to a seaside hotel where some rather unusual people are staying.

While the investigation centres on the Jefferson family and their entourage, Miss Marple's hunch about a second killing proves all too tragically justified.