Tommy Beresford and Tuppence Crowley, after their first foray into amateur crime-solving in Christie's earlier novel The Secret Adversary, are now happily married to each other--but both are finding the settled life a little boring. When the opportunity arises to go undercover disguised as professional detectives, the newlyweds seize the chance. While helping Scotland Yard infiltrate a ring of international spies, they also take on every chance client who comes through the door. In the process, they succeed in recovering a stolen pink pearl, finding out who poisoned a box of chocolates, and tracing how a murderer vanished into thin air on a golf course, among other thrilling adventures.