the u.s. has not yet entered world war ii when kindly stamp dealer otto becker (conrad veidt) is unexpectedly visited by his twin brother, baron hugo von detner, the new german consul to the u.s. and one of the leaders of a spy ring engaged in sabotage. the brothers have not seen each other in years, but now von detner wants to use becker's shop to transmit and receive secret messages. becker refuses, until von detner threatens to have him deported back to germany as an illegal immigrant and reveals that becker's assistant, miss harper (dorothy tree), is actually a german agent.