The plaintiffs in a sensational breach of promise suit are wealthy social climbers Barton and Delphine Lambert, suing on behalf of their beautiful daughter, Zillah. The defendant is Zillah's alleged fiance, brilliant young architect Killian Melville, who adamantly declares that he will not, cannot, marry her. Not even to his counsel, distinguished barrister Sir Oliver Rathbone, will Killian explain his rejection of rich and charming Zillah. Utterly baffled, Rathbone turns for help to his old comrades in crime - Monk, the private investigator who knows his city like the back of his hand, and fearless nurse Hester Latterly. But even as they scout London for clues, from Mayfair to sordid Devil's Acre, the case suddenly and tragically ends. An outcome that no one - except a ruthless murderer - could have foreseen.