On her journey to visit her aunt's family in Monte Carlo, orphaned heiress Lily Fairfield makes the acquaintance of secret serviceman Hercules Popeau and his friend Captain Angus Stuart. When Lily arrives at her aunt's house, she finds an aristocratic family fallen on hard times. More worryingly, the discovery of a dead body near the house sparks off a chain of events which threatens to endanger Lily's life. With nowhere to turn, she appeals to Hercules Popeau for help. But can even his dexterity prevent further tragedy?

Originally published in 1920, this vintage thriller by the author of The Lodger features a memorable French detective, thought to be a partial inspiration for Agatha Christie's Hercule Poirot.