Holmes and Watson board a passenger train bound from London to Edinburgh, to guard the Star of Rhodesia, an enormous diamond worth a fortune belonging to an elderly woman of wealth; but within the first hour of the trip, the woman's son is murdered and the diamond stolen and any of the passengers in their car could be the killer thief.

• Universal Pictures
• Basil Rathbone
• Nigel Bruce
• Alan Mowbray
• Dennis Hoey
• Renee Godfrey
• Frederick Worlock
• Mary Forbes
• Skelton Knaggs