At a suburban train station, private secretary Joyce Willecombe bids farewell to her wealthy boss's blind daughter, Lorna Murchison, and boards a train bound for the city. After the train gets underway, Joyce notices a car chasing it to the next stop, where the car's male passengers, Gus Hadder and Vince Marley, then separately board the train. Joyce notifies the conductor when she notices one of the men carrying a gun, and the conductor wires ahead to Union Station to arrange for station police lieutenant William Calhoun to meet her on arrival. Although Bill expresses his doubts about her claims, Joyce's suspicions are heightened when she sees Hadder and Marley deposit a suitcase in a locker and mail the key in an envelope. Bill retrieves the suitcase, which Joyce identifies as belonging to Lorna. Bill realizes that Lorna must have been kidnapped and sends for Inspector Donnelly from the city police, and Lorna's father Henry Murchison, who, although he has not yet received a ransom demand, does not want the police involved. Joyce becomes angry because the kidnappers manage to escape, so she stays at the station to help identify them when they return. When the kidnappers finally make first contact with Murchison at the station, Joyce identifies them. Bill and his men surreptitiously follow Hadder on the elevated trains to a freight depot, but Hadder becomes suspicious and runs into a cattle stockyard, where he is killed by a stampede of cattle frightened by the police gunshots. Donnelly and Bill stifle news of Hadder's death so as not to alarm the other kidnappers, and then set up plainclothesmen in the station to watch Murchison's arranged meeting. Although the kidnappers fail to make contact at the appointed hour, Joyce sees Joe Beacom, the mastermind, whom she recalls as the driver of the car, and follows him. She then writes down the license plate number of his car, while the police capture Marley. Terrified when the police threaten to push him in front of a train, Marley reveals the address where Lorna is being held. Beacom, meanwhile, tells his girl friend, Marge Wrighter, that he intends to kill Lorna after he gets the ransom. By the time the police raid his apartment, he, Marge and Lorna have gone. When Bill visits Joyce to let her know that Lorna is alive, Joyce finds herself caring for him, even though he once seemed more interested in the logistics of the kidnapping than in actually saving Lorna. That same night, a patrolman identifies Beacom and attempts to arrest him, but Beacom kills the policeman and ruthlessly shoots Marge, leaving her in the street as he escapes with Lorna. In the hospital, Marge tells Donnelly, Calhoun and Murchison about Beacom's plan to kill Lorna. Beacom, meanwhile, takes his terrified captive into the municipal tunnels below the city, which feed into Union Station. After placing her in a freight cart where she is in danger of being electrocuted by live wires, Beacom wends his way up to the station, dressed as a conductor. Murchison arrives in the morning for the next ransom drop off, and Beacom quietly takes a parcel clerk hostage. Murchison then receives a telegram advising him to give the suitcase of money to the messenger, who then drops off the suitcase for the parcel clerk. When the clerk appears to send the messenger away with the same suitcase, both Bill and Joyce notice that the suitcases have merely been exchanged. Beacom then shoots Bill and escapes into the tunnels. Despite his injury, Bill follows Beacom into the tunnels, and shoots the kidnapper in the process. Using a utility phone, Bill gives Donnelly and the police his location. Bill then wounds Beacom a second time, and the kidnapper drops the money and staggers toward Lorna. Bill kills Beacom as the kidnapper aims for Lorna, and she is saved. As father and daughter are reunited, Joyce tends to Bill's shoulder wound, and announces her intention of looking after him for a long time.