Joan, an earnest little orphan who lives in an asylum near the World War I training camp at Plattsburg, reads the story of "Joan of Arc" and soon imagines that she is the reincarnation of the peasant-soldier. As she sits in the cellar reading, she hears voices plotting against the government. She thinks the voices are from another world but they actually belong to a group of German spies. The agents plan to acquire the important invention of a young man named Ingleton, who is staying at the camp under the guardianship of Captain Lane. Joan relates this information to the captain, with whom she is in love, but he at first refuses to believe her. Later, however, he learns that the plot is real, and with Joan's help, he captures the spies.

A resourceful young girl struggles to free herself from slum life.