A bookish historian is married to a steely Southern belle who raises horses, an animal that he doesn't care for. However, the cute young neighbor girl doesn't feel that way about him and makes no bones about letting him know it.
Johnny Farrell is a gambling cheat who turns straight to work for an unsettling casino owner Ballin Mundson. But things take a turn for Johnny as his alluring ex-lover appears as Mundson's wife, and Mundson's machinations begin to unravel.
When the fabled Star of Rhodesia diamond is stolen on a London to Edinburgh train and the son of its owner is murdered, Sherlock Holmes must discover which of his suspicious fellow passengers is responsible.