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In order to save her sister from a pack of rebels, Nina Garcia (Edith Johnson) agrees to spy for them. She makes her way to an army hospital where Dr. Ralph Hamlin (Harry Carey) is working hard at finding a cure for gangrene. Nina's spying is discovered, but before she can be arrested, she experiments on herself to help Hamlin's efforts. She recovers just in time to be sent in front of the firing squad. The doctor can't get her pardoned, but the U.S. troops arrive just in the nick of time. The doctor gets his chance to throw in a few punches (it wouldn't be a Harry Carey film without the fisticuffs), and Nina is saved.