At the Hunt Ball in Westhampton, Sheila Delaney dances the night away with a stranger--a man who wanted only to be known as Mr. X. At the end of the evening, he departs as mysteriously as he appeared... Months later, private investigator Anthony Bathurst is approached by the Crown Prince of Clorania over a nasty blackmail case... At the same time a sea-side dentist finds that the girl he was treating has been found dead, apparently injected with cyanide... The three events proved to be intimately related, and Anthony Bathurst and Chief Detective-Inspector Bannister find themselves on the trail of an exceptionally ruthless murderer.