Pierre Duval, a poor Frenchman living in a New York boardinghouse, is barely able to support his son Jacques's studies in a Parisian art school. When war breaks out, Jacques returns home, unaware that a disreputable art dealer named Raoul Vaux has tricked him into smuggling stolen paintings into the United States, hidden among his own works. The Secret Service suspects that Jacques is Vaux and send their agent, Ellen Ingram, to entrap him. She goes to live at the same boardinghouse as Pierre and Jacques and soon becomes friendly with them. To support himself and his son, Pierre takes on an extra job as a nightwatchman at a museum. When Jacques learns through Ellen that "Vaux" is an art thief who plans to steal some paintings from the museum where Pierre works, he tries to prevent the theft, but is arrested himself instead. Finally, the real Vaux is captured, and Pierre and Jacques receive a reward from the French government for helping to recover stolen paintings. Financially secure, Jacques is now able to marry Ellen, with whom he has fallen in love.