What connection exists between a medieval Dutch painter like Hieronymus Bosch and a sinister series of murders in London in 1895? None, says Inspector Lestrade of Scotland Yard. But Sherlock Holmes disagrees. Together with Dr. John Watson, he investigates in sinister opium dens and a mysterious moated castle. Along the way, he meets a shady opera singer, an enigmatic gnome, and a derelict abortionist.