London, 1941. The city is in blackout, besieged by nightly air raids from Germany. Two strangers are about to meet. Between them they may alter the course of the war. While the Blitz has united the nation, there is an enemy hiding in plain sight. A group of British citizens is gathering secret information to aid Hitler’s war machine. Jack Hoste has become entangled in this treachery, but he also has a particular mission: to locate the most dangerous Nazi agent in the country. Hoste soon receives a promising lead. Amy Strallen, who works in a Mayfair marriage bureau, was once close to this elusive figure. Her life is a world away from the machinations of Nazi sympathisers, yet when Hoste pays a visit to Amy’s office, everything changes in a heartbeat.