Howard Graham, an American engineer, finds himself entangled in a dangerous web of espionage while on a business trip in Istanbul during World War II. Unbeknownst to him, his work on military technology makes him a target for Nazi spies. One evening, as he is enjoying a quiet dinner with his wife, Stephanie, and his Turkish contact, Kopeikin, an assassination attempt is made on his life. The attempt fails, but it sends Graham into a paranoid state of fear and uncertainty. After seeking refuge with the local authorities, including Colonel Haki and Kopeikin, it becomes evident that getting back home safely will not be easy. He is persuaded to take refuge on a Turkish steamer bound for Genoa.

As the ship departs from Istanbul, Graham realizes he is trapped aboard with a cast of mysterious, potentially dangerous passengers. Among them are a mysterious dancer named Josette, her male companion Kuvetli, and other individuals whose allegiances are uncertain. With enemy agents possibly lurking among them, Graham fears for his life and begins to suspect everyone around him. His anxiety heightens as he discovers another assassination attempt might be imminent. Unarmed and in unfamiliar territory, Graham must rely on his wits to navigate through the murky waters of international espionage and survive long enough to return to his wife and the security of home. He is continuously haunted by the shadows that seem to be closing in, unaware of who he can trust within the confines of the ship.