Set during World War I, the novel follows an espionage conflict that grows from a single coded letter into a test of loyalty and moral resolve. Evelyn Erith, working at an intelligence bureau, discovers a mysterious yellow envelope containing a cipher and, with Clifford Vaux’s cautious approval, begins tracing its origin. The trail leads to Herman Lauffer, while the sudden involvement of another agent, Cassidy, complicates the pursuit and heightens the stakes. Through this tense investigation, the novel explores the cost of secrecy, wartime duty, and Evelyn’s determination to assert her competence within a male-dominated intelligence world.
