During a rebellion in Mexico, Nina Garcia, a diplomat's daughter, is forced to become a spy for the revolutionaries. She works as a nurse in a military hospital and steals papers for the rebels, but officials finally discover her involvement in enemy espionage. Just as soldiers arrest her, she performs an experiment on herself, hoping to prove the worth of Dr. Ralph Hamlin's serum for gangrene. Unimpressed by her bravery and unmoved by Ralph's pleas for a pardon, the government orders her shot after her recovery from the injection. Finally, United States troops arrive and save Nina from execution.