Sherlock Holmes and Dr. Watson look into reports that a huge, vicious hound has killed Lord Charles Baskerville and that Lord Henry Baskerville is the next to be killed.

Tenor Mario Monti is searching for his wife Bianca's daughter, who is believed to be dead. Before Mario, Bianca was married to Carlo Scarpia, Mario's patron. When Carlo discovered that his wife and Mario were having an affair, he left them both and, as he was leaving, told Bianca that their daughter Mary had died. In reality, she grew up without knowing her real parents. Mario tracks Mary down in Munich, where she works as a ballerina at the State Opera.