Terror by Night

Terror by Night is a 1946 Sherlock Holmes film, the thirteenth to star Basil Rathbone and Nigel Bruce and was directed by Roy William Neill. The story revolves around the theft of a famous diamond aboard a train. It is one of four films in the series in the public domain.

In London, Vivian Vedder Renee Godfrey verifies that a carpenter has completed a coffin for her recently deceased mothers body, which she is transporting to Scotland by train. She boards the train that evening, as do Lady Margaret Carstairs Mary Forbes, who owns and is transporting the famous Star of Rhodesia diamond Lady Margarets son Roland Geoffrey Steele Holmes, whom Roland has hired to protect the diamond Inspector Lestrade Dennis Hoey, who is also worried about the diamonds safety and Watson and his friend Major DuncanBleek Alan Mowbray. Holmes briefly examines the diamond.Shortly afterward, Roland is murdered and the diamond is stolen. Lestrade, Holmes, and Watson learn nothing conclusive in questioning the other passengers, and Holmes is pushed out of the train, nearly to his death, but he climbs back inside and discovers a secret compartment in the coffin carrying Miss Vedders mother. He suspects that one of the people on the train is the notorious jewel thief Colonel Sebastian Moran. ........

Source: Wikipedia