Ethel Andrews is interested in settlement work. Her father refuses to cooperate with her. Ethel kidnaps her five-year-old brother Archie and places him in a tenement as an object lesson. To make the kidnapping appear the work of criminals, Ethel sends her a father a note demanding $10,000. Gangsters learn of the plan. Andrews engages Madelyn Mack, a girl detective, to find his son. Madelyn unearths several clues, among which are fragments of a tin soldier belonging to Archie. She strongly suspects Ethel of being implicated in the matter. Ethel, regretting her rash act, goes back to the tenement to bring Archie home. The gangsters capture them both, and send a note to Andrews telling him his son and daughter are prisoners. One of the gangsters shoots the note into the Andrews' library with a sling shot, just as Madelyn is telling the father of her suspicions concerning Ethel. The note upsets her theories. Madelyn discovers that the paper on which the gangsters' note is written has contained powdered Jasco berry, an Oriental drug used in cigarette form. Later, she succeeds in tracing Ethel and Archie to the tenement, but finds them gone. Passing a crowd collected on a corner, Madelyn scents the odor of Jasco berry and finds the man who is smoking it. She follows him and discovers the cottage in the suburbs where Ethel and Archie have been taken. She slips into the house and enters the room where the two are confined. Discovering a telephone wire outside the window, Madelyn taps the line with a pocket phone and summons assistance. She is discovered by the gangsters, who are just about to break into the room when the police arrive. A desperate battle ensues, which ends in the capture of the kidnappers. Andrews presents Madelyn with a check for $10,000 for her splendid work. The detective gives the check to Ethel for settlement use, but Andrews, returning the check, smilingly donates the money himself.—Moving Picture World synopsis