What's behind a series of mysterious deaths among the favourite concubines of Sultan of Turkey, Abdul Hamid II? Suspecting a plot against himself, the Sultan has called on Sherlock Holmes to investigate. However, as a man, the detective is clearly unable to penetrate the exotic enclosed world of the harem, so he reluctantly enlists the help of his landlady, Mrs Hudson. Together with Dr Watson, they travel across Europe by Orient Express to Constantinople, on the way encountering Holmes's old enemy, Baron Mauterpuis.
Once ensconced in the harem, Mrs Hudson has to adjust to the strange new world she finds there, rife with jealousy and superstition. Holmes has assured her that she is in no danger, but, while trying to unravel the tangled web around the deaths of the concubines, Mrs Hudson uncovers some alarming evidence regarding the Baron, that puts her in mortal danger.
The medley of characters in this engrossing novel includes the formidable Abdul Hamid II himself, the sweet young Princess Naime, a glowering eunuch called Bashir, Mrs Hudson's lively little French maid Madeleine, a Russian diva, a homely English governess, a malevolent little boy and a tiger named Guzellik.