Sherlock Holmes uncovers a plot to murder the heir to a country estate.

In turn-of-the-century England, mystery shrouds the deaths of the hereditary heads of the Baskerville estate. According to legend, a vicious hound stalks the descendents of Sir Hugo Baskerville in order to avenge the death of an abducted peasant girl. Latest to assume the heritage is young Sir Henry, who arrives from Canada after the mysterious death of his uncle. Suspecting that murder is afoot, the family physician, James Mortimer, sends for Sherlock Holmes and his associate, Dr. Watson, to investigate. Holmes dispatches Watson to the moors of Dartmoor to protect Sir Henry, while the great detective lurks in the background, undercover. Before Holmes's appearance at the estate, Watson meets neighbors John Stapleton and his charming half sister Beryl, the irascible Frankland, and the mysterious butler Barryman and his wife. As the bloodcurdling baying of the hound drifts across the moors, Mrs. Barryman's escaped convict brother is murdererd while wearing Sir Henry's clothes. This prompts Holmes to decide that he must set the stage for attempted murder in order to trap the killer, and thus he announces that he is leaving for London. That night, on the mist-shrouded moor, the ghostly figure of the ferocious hound rushes toward its victim, Sir Henry, but Holmes and Watson shoot the beast before it can kill its target. Afterward, in the great hall of the manor, Holmes unmasks the hound's master, John Stapleton, as a distant relative of Sir Hugo and proves that he was jockeying to place himself in line to inherit the Baskerville estate.