'The Man With the Twisted Thumb' is an elegant detective short story by Anthony Berkeley, first published in 1933. The narrative begins on a bench at the Monte Carlo casino, where an incredible similarity leads to the accidental swap of two small black handbags. One belongs to Veronica Steyning, a young English governess, and the other to a mysterious woman of Spanish appearance. Inside the mistakenly taken reticule, Veronica discovers a coded message, setting off a chain of unpredictable events.

What seems to be a minor everyday mishap becomes the starting point of a spy quest and an investigation, where the key guide to uncovering a criminal conspiracy and real identities is a single physical trait—a man with a deformed thumb. The author masterfully combines his signature irony, psychological intrigue, and the classic canons of Golden Age detective fiction, demonstrating how easily the most deceptive facades can crumble.