Miss Mary Marstan receives through the post once a year a large pearl without any clue as to the sender. When her mysterious correspondent requests a meeting, Holmes and Watson start out on a case. A terrible death and vanishing treasure lead to an epic pursuit through the dawn streets and later along the River Thames. The cast of characters include the unfortunate Sholto twins, the mongrel Toby, and the wooden-legged man, as the fire and blood of Mutiny-torn India throw gigantic, distorted silhouettes across late Victorian London.