Miss Mary Morstan receives a large pearl once a year, by mail, without knowing anything about its sender. When her mysterious sender asks to meet her, Holmes and Watson undertake to help her.
A gruesome death and the disappearance of the treasure lead to a monumental pursuit through the dimly lit streets and later on the waters of the Thames. The story includes the unfortunate twin brothers Soltos, the dog Toby, and a man with a wooden leg, as the rebellion in India, sealed with fire and blood, casts its gigantic, distorted silhouettes over Victorian London.