The great detective's melancholy mood is lifted by the arrival of attractive Mary Morstan at 221B Baker Street. Mary's father vanished 10 years ago. Four years later she bagan to receive, annually, a large, lustrous pearl. Now she has had an intriguing invitation to meet her unknown benefactor and urges Holmes and Watson to accompany her. The duo are confronted with a case that includes a wronged woman, a wooden-legged ruffian, hidden treasure, and a love affair.