Serena Frome, the beautiful daughter of an Anglican bishop, is being groomed for the intelligence services after a brief affair with an older man during her final year at Cambridge. She is sent on a secret mission and comes in contact with a promising young writer, Tom Haley, and while at first she loves his books, she then comes to love the man, and while trying to maintain her undercover life she breaks the first rule of espionage, trust no one.