450 from Paddington: Two trains briefly draw alongside each other as they race past a country house and --to her horror-- Mrs. McGillicuddy witnesses a murder in a passing train car. But no body is found, and the police decide Mrs. McGillicuddy must have dreamed the incident. Miss Marple believes otherwise and persuades a bright young friend to help her investigate.

They do it with mirrors: Miss Jane Marple finds herself investigating murder when, at the urging of Ruth Van Rydock who has premonitions of foul play, she visits Stonygates, home of her friend Carrie Louise Serrocold and a treatment center for juvenile delinquents.