In the dead of night on June 12, 1942, four sailors climb from their German U-boat and make their way toward the coast of Long Island, NY. From there, they board the Long Island Railroad heading into Manhattan. One of the men, Cal Miller, is a US citizen, making him the perfect candidate for a special mission to infiltrate the States and gain access to key economic targets he can destroy. Three seats ahead, Lexie Smithfield ponders her future as a nurse at Bellevue Hospital and wife to her fiancé Russell Thompson. A brief encounter with Cal Miller on the train leads to an unlikely friendship, and ultimately to the fearsome discovery that this handsome, kindly man is not who he appears to be. When Russell is given an opportunity to work overseas, Lexie reluctantly encourages him to go. But his absence leaves Lexie alone in a strange city where her path becomes increasingly darkened by her unwitting connection to the German saboteurs. As the spies lay plans to destroy American factories and bridges, it becomes clear that only two people can stop them. One is a catatonic patient at Bellevue who must be strapped to his bed and sedated. The other is Lexie herself, a young woman who longs only for the security of marriage while ministering to the war's physically and emotionally wounded.