The Unlikely Spy is a 1996 spy novel written by Daniel Silva, set during World War II. While some of the characters and events are fictional, the book is based on the real-life attempt by the Allies to use British intelligence to cover up the true plans for D-Day. The deception plan was called Operation Fortitude, and Double Cross also played a role. Specifically, the book has a backdrop (a subset of Fortitude referred to as Fortitude South). Source: Wikipedia (en)