Fourteen-year-old Judy Widdell, who lives with her aunt, actress Jessica Widdell, has an active imagination, and communicates with her good friend Nancy Fairchild, secretary to mystery writer Archibald Fenton, in code. Because she disapproves of Nancy's influence on Judy, Jessica forbids her niece to see her friend. Before Nancy leaves town with her employer, Judy begs Nancy to meet her at the house that Jessica has rented out to reduce expenses. While Judy waits for Nancy, however, Jessica appears. Although Judy tries to keep out of her way, Jessica spots her and hurrying to punish her, slips and falls to her death. Judy feels as if she had murdered her aunt and runs away, leaving Nancy a note telling her where she has gone. Upon her arrival in the country, Judy buys a squirt gun, which she fills with red ink. Looking for a hideout, she encounters Tom Fenton, a boy about her age, who is an amateur astronomer and Archibald's younger brother. After he shares his dinner with Judy, he suggests that she spend the night in the shack where he keeps his telescope. Meanwhile, Agatha, Jessica's maid, believes that Judy was kidnapped and calls the police. In the country, Tom gets Judy a room at his boardinghouse by pretending that she is his sister. He offers to retrieve her mail in town, where Nancy overhears him use Judy's pseudonym. She questions Tom, but he mistakenly thinks she is the person Judy is avoiding. Archibald, who is also in town, demands to know why Judy is posing as Tom's sister and tries to turn her in to the constable. She shoots Archibald with the water pistol and he faints, believing that he has been wounded. When Tom returns, he tells Judy that he plans to earn the reward for finding the missing girl, and Judy confesses that she is the missing girl and is guilty of murder. When he hears this, Archibald immediately fetches the sheriff. After a series of mishaps, Jessica's death is revealed to be an accident and Judy agrees to wait for Tom to finish college so that they can be married.