When medical school student Tom Wright catches Bob Farrell stealing money from him, Farrell is expelled and joins a gang of smugglers. Soon after his graduation, Dr. Wright is a passenger in a taxi that hits a young woman. Wright insists on taking her home to treat her injuries, but after discovering that the house is a gambling establishment, he is falsely accused of murdering a policeman during a raid. At his trial, Wright is convicted on Farrell's testimony and on circumstantial evidence. While he is in prison, Wright asks his sister Nell to have detective James King follow Farrell. After a series of misadventures involving the smuggling of Chinese citizens, King learns that Farrell is the actual killer and that he has kidnapped Nell and hidden her in a cave. Wright then escapes from prison and follows King's trail to the cave. In a subsequent struggle between Farrell and Wright, Nell tries to intervene but is thrown into a barrel by Farrell's men. Farrell plunges to his death from a precipice over Niagara Falls just as the barrel is thrown down. Nell is rescued, unconscious, but alive by King.
Exterior scenes in the film were shot on location in New York City, New York State, and Niagara Falls, Canada. The film was also known as Over Niagara.