Miss Winters is a dancer with the Tommy Dorsey Orchestra and is asked to secretly transport a prototype magnetic mine to Puerto Rico. She thinks that she is working for the US Government, but fails to see why she would be involved.
Humble stamp dealer Otto Becker has little to do with international politics, so when he receives a surprise visit from his estranged twin brother and Nazi spy, Baron Hugo von Detner, his world is thrown into turmoil. Threatening Becker with deportation, Hugo forces him to use his shop as a front for espionage.