S4·E1 The Sign of Four

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.