S1·E3 The Body in the Library (3)

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.