The stone of the title is an enormous diamond plundered from an Indian shrine after the Siege of Seringapatam. Given to Miss Verinder on her eighteenth birthday, it mysteriously disappears that very night. Suspicion falls on three Indian jugglers who have been seen in the neighborhood. But all is not as it seems; dark secrets lurk behind respectable façades, and the trail of clues leads Sergeant Cluff in quite a different direction.