The great hypnotist Professor Montserrat has developed a technique for controlling the minds, and sharing the sensations, of his subjects. He and his wife Estelle test the technique on Mike Roscoe, and enjoy 'being' the younger man. But Estelle soon grows to love the power of controlling Roscoe, and the vicarious pleasures that provides. How far will she go, and can the Professor restrain her in time?
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.