When Caythorpe's niece calls in distress, claiming her uncle is trapped in a locked strong room, Tarleton rushes to the scene and discovers that he has died, possibly of heart failure but more likely as a result of foul play. The finger of suspicion points at those who stood to gain from his demise, including an American businessman, an English countess, an Indian princess, and a mysterious Mexican with a black beard.
With motives and secrets intertwined, Tarleton must unravel the threads of deceit to catch a cunning killer in this classic mystery which was first published in 1927.