Investigation of a Hit and Run follows two officers as they investigate a hit-and-run accident from initial reports to the questioning of witnesses and the interrogation of the suspect, an eighteen-year-old boy nicknamed Pumpkin, along with his girlfriend and brother. A number of factors complicate the case: the suspect was without a driver's license; he reported the car stolen to cover himself; he could not be persuaded to confess; and the girlfriend is pregnant. The police use considerable pressure on the girl, and treat her eventual statement as though it were a confession.