In London, Lady Margaret Carstairs (Mary Forbes) and her son, Roland (Geoffrey Steele), engage renowned detective Sherlock Holmes (Basil Rathbone) to accompany them back home to Scotland as protection for their priceless gem, the Star of Rhodesia. When Roland turns up murdered and the Star disappears, Holmes and his friend Dr. Watson (Nigel Bruce) investigate -- only to discover another murder, and a strange connection with Watson's acquaintance Maj....

In the harsh, wintry woods of rural Quebec, Bruce, a down-on-his-luck snowplow operator, accidentally kills a man during a drunken night joyride. Stricken with panic, he hides the body and takes to the deep wilderness in hopes of outrunning both the authorities and his own conscience. But as both begin to close in, Bruce falls apart mentally and morally and mysteries unravel to reveal who he was before the accident.