Two years later. America is wrestling with whether to enter the growing war. Charles’s estranged wife and six-year-old daughter, Emma, now live in a quiet brownstone in the German-speaking New York City neighborhood of Yorkville, where support for Hitler is common. Charles, just out of prison, struggles to put his life back together, while across the hall from his family, a kindly Swiss couple, Trudi and Willi Bauer, have taken a liking to Emma. But Charles begins to suspect that they might not be who they say they are.
As the threat of war grows, and fears of a “fifth column”—German spies embedded into everyday life—are everywhere, Charles puts together that the seemingly amiable Bauers may be part of a sinister conspiracy. When Pearl Harbor is attacked and America can no longer sit on the sideline, that conspiracy turns into a deadly threat with Charles the only one who can see it and Emma, an innocent pawn.