For years after her father's disappearance, the beautiful Miss Mary Morstan receives anonymously every year one large and valuable pearl. When, finally, an invitation arrives to meet the mysterious pearl-giver, Mary Morstan seeks Holmes's advice, and he begins to unravel some remarkable clues, including a poison dart and a man with a wooden leg. What Holmes finds is an old soldier who is determined to punish those who betrayed him and his friends by stealing their oriental treasure.