In a bustling 1920s London, a mysterious individual impersonates a high-ranking official in the British government, unleashing a series of hilarious and tense events. It all begins when a mystery novelist, weary of routine and seeking inspiration, stumbles upon a lost letter that leads him to believe in the existence of a significant state secret. Unbeknownst to him, he gets caught up in a web of espionage, intrigue, and an identity game that will change his life forever.