Peter Mullaney, the son of Irish immigrants living on the East Side of Manhattan, has one ambition in life: to become one of New York's Finest. He goes to the Police Training School and is about to be rejected for not meeting the height qualification when he demonstrates his prowess in a fight. The commissioner then decides to give Peter a chance to make the force, if he scores well on the written examination. Peter declares the Tropic of Capricorn to be in the Bronx and fails to pass; the commissioner, however, allows him to wear the uniform for one night in order not to disappoint Peter's girl, Judy McNulty. Walking the beat with Officer Gaffney, he becomes involved in preventing a robbery, during which Gaffney is shot. Peter comes to his aid and captures the robbers, being himself hurt in the process. In the hospital, the commissioner, on account of his bravery, pins a shield on him, and Peter and Judy make plans to be married.