As the Blitz continues to ravage London, Ellie McDonnell is approached by British Intelligence officer Major Ramsey with a new assignment. She is to travel under an assumed identity to the port city of Sunderland and there await further instructions. Ellie heads north, her safecracking tools in tow. But before she can rendezvous with the major, she witnesses an unnatural death. A man falls dead in the street in front of her, with a mysterious missive clutched in his hand. Ellie's instincts tell her that the man's death is connected in some way to her mission. Reunited with Major Ramsey, the pair discovers that the dead man had ties to a counterfeiting operation, supplying German spies with fraudulent British currency to use in their operations. Even more troubling, it becomes apparent someone high-up in the operation is helping to smuggle those spies into England across the North Sea.