At an auction of rare stamps, confidence man George Zelger, who goes by the name Strauss, and his henchman, Louis Reese, are interested in some valuable stamps that have been printed with the Statue of Liberty upside down. The auction begins, and Zelger wins the bidding for the stamps by offering $100,000. He goes to the desk where Clara Kelso, the auction director's assistant, who actually works for Zelger, slips him the stamps. Louis then takes the stamps into the hallway and places them in an envelope addressed to Zelger's New York apartment. After he drops the envelope into the mail slot near the building's elevators, Louis returns to his seat at the auction, which is still in progress. Meanwhile, Clara has replaced the valuable stamps with forgeries, which an astute collector soon recognizes. Later, Clara and the other members of the gang, Frank Forenti and Bruno Antista, decide to retrieve the envelope from the mail before it arrives at Zelger's. When mail carrier Bill Mannerson and his partner, Eddie Waltch, arrive at the building, Clara begs them to give her the envelope. Although Bill explains that retrieving a letter from the mail is a federal offense, he gives it to her on condition that she meet him when she gets off work. Clara returns to her office, just as the police determine that the theft must have taken place during the auction. When the investigator notices the mail slot in the hall, he decides to go to the post office to examine Bill's mailbag. Bill begins to suspect that Clara was involved in the crime, which has now been reported to the postal authorities. After work, Bill goes to the law firm where Clara said she was employed and meets the real secretary, April Shaughnessy. When he realizes that Clara lied to him, Bill asks April out instead. While out for a drive with Eddie and his girl friend "Bubbles," Bill notices that they are near the address that was on the envelope he gave to Clara. Meanwhile, at Zelger's, Clara demands her cut of the $10,000 that Zelger is asking for the stamps. When he notices Bill outside, Zelger invites him in, and Clara runs for the door. Bill follows her out to the street, where Frank suddenly pulls his gun and forces him into a car. Witnessing Bill's abduction, Eddie, Bubbles and April follow the car to Hopton's Boat Landing. There, Bill escapes when Clara and Frank board Zelger's yacht. Later, Bill reports his findings to postal authorities, who conclude that Zelger was double-crossed by members of his own gang. At her boss James Seeley's office, Clara eavesdrops while James speaks with Inspector Delany. When April sees Clara leaving the office, she recognizes her and follows her to the subway, where she has hidden the stamps in a locker. April then trails Clara to Bruno's apartment, and he takes money from his wall safe to pay for the stamps. When Louis and Zelger appear, Clara draws her gun and shoots them. Bill struggles with Frank, and when Clara tries to escape with the money and the stamps, the inspectors grab her. April then arrives, and Bill invites her to go on a real date.