American heiress Henrietta Doran (known as Hatty) marries Lord St Simon, but she vanishes without trace on her wedding day, leaving London agog. Later, the police find her wedding dress in the Serpentine, a lake in a London park, with a note in the pocket of the dress. While investigating the case, Holmes suffers from nightmares, which he sees as a factor in the mystery.

Holmes investigates when a man dies and the manuscript of his recently-completed book is stolen. He has to discover who was behind an unusual proposal to buy a house and all of its contents.

The police are baffled by the murder of Willoughby Smith, and Inspector Hopkins looks to Holmes to solve the case.

The Mazarin Stone, a famous jewel, acts as a magnet for crime. Holmes investigates the latest and perhaps most curious episode in its adventures.