An innocent couple fights off Nazi agents on a speeding train.

At Union Station in Los Angeles, Nazi spies Hugo and Frieda Molte and their associate, Herman Krantz, have a dilemma. They have planted a time bomb, set to explode at 10:22 p.m. in a bag that Herman has deposited in the station's luggage checkroom. Another identical bag, containing evidence which could lead to the Moltes' execution, is also in the checkroom, but they dare not try to recover it as they are being watched. Meanwhile, famous war correspondent Bruce Grant, and his photographer, Stew, are trying to locate Jane Thornwald, the daughter of their publisher, in the station. Jane, whom Bruce and Stew have never met, and her maid, Millie, arrive at the station to travel north to Jane's father's estate. By coincidence, Millie is Herman's girl friend, and he persuades her to claim the bag containing the evidence, intending to collect it from her when he visits her over the weekend. However, Herman gives Millie the wrong claim stub, and the bag with the bomb goes on board the train with her. As Bruce is anxious to talk with Jane's father, he and Stew also board the train, along with the Moltes, who plan to remove the evidence from the bag during the journey. Meanwhile, Herman reports back to the local Nazi spy chief that they will soon have the evidence bag and discards the other stub. After another agent recognizes that number as belonging to the bag containing the evidence, Herman sends a coded telegram to Frieda, under her code name Mrs. Harrison Brown, on board the train, advising her that if they open the bag, they and many others will be killed. Bruce, meanwhile, invites Jane for a drink, and although he introduces himself using a false name, she recognizes him from a photograph on one of his books, Darkest Germany , which she happens to be reading. Bruce remembers meeting the Moltes in Germany and hearing of their evil reputation. In Jane's compartment, Molte, meanwhile, disturbs an Italian spy who is trying to open the bag and stabs him to death, then stuffs his body in a closet. He is about to leave with the bag when a porter interrupts him. Bruce then enters, finds the body and plants it in Molte's compartment. The Moltes, who have yet to receive Herman's telegram, wire the head spy that Bruce and Jane are on the train, but the chief orders that nothing happen to Jane as they will no longer be able to blackmail her father and collect $200,000. Later, in the dining car, Bruce explains to Jane that her father has suddenly suspended publication of a series of articles Bruce has written about Nazi Germany. Meanwhile, the Moltes discover the dead Italian in their compartment and move him to Bruce's. Frieda then tricks Jane into leaving her compartment so that her husband can get to the bag, but Bruce and Stew, aware that the bag holds secrets, get there first and take it to their room. Bruce cannot open it, however, and leaves to find a pocket knife. During his absence, Molte comes in, struggles with Stew, stabs him and takes the bag. Bruce tends to Stew's wound, but arouses the suspicion of the train conductor, who wonders if Bruce could have been Stew's attacker. When the Italian's body falls out of Bruce's closet at his feet, the conductor takes Bruce into custody, but Bruce manages to escape. Molte, still unaware of its contents, then tries unsuccessfully to open the bag. Suddenly, the train pulls to a stop and police officials and a doctor come on board. Herman's telegram finally reaches Frieda, but before she can decode it, Bruce holds them at gunpoint, then silently decodes the message himself. Five minutes before the bomb is to explode, Bruce permits the Moltes to leave the train with the bag. They run off and are blown to bits. Jane's statement clears Bruce. Herman is arrested at the station while trying to retrieve the evidence bag, and Nazi headquarters is raided and phony composite photographs of Jane in the company of Hitler and Göring, which are being used to blackmail her father into dropping Bruce's articles, are found. Later, Thornwald orders the immediate publication of the articles while Bruce writes a dedication in Jane's copy of his book, "To my wife, Jane."