When Sir Charles Baskerville is found suspiciously dead, his friend, Dr. James Mortimer asks Sherlock Holmes to look into the death. While the cause of death is determined to be a heart attack, Mortimer suspects foul play and fears that Sir Charles's nephew and sole heir, Sir Henry Baskerville, may be in danger next. Supposedly the family's ancestor, Hugo Baskerville, sold his soul to the devil, and the family has been haunted by a large spectral hound ever since.