Young Mary Tillet is forced to find a new place to live due to her London home being bombed during World War II. Her tobacconist landlord, Jack Rawling, tries to help her turn her new apartment into a home. Meanwhile, the newspapers are reporting news of the 'London Blackout Murders', a murder spree being committed against a ring of suspected Nazi spies, and Mary must determine if her kind landlord is an assassin.