A story of the motorcycle cops of the traffic-division of the Los Angeles Police Department. Ken Foster, a trainee, is engaged to the sister, Jean Collins, of motorcycle policeman Larry Collins, who is taking part in the investigation of a hit-and-run killing the police believe was a deliberate murder. Sighting a stolen car used in the killing, Larry pursues it and is killed by the driver. Ken is taken from the training academy and given the assignment of impersonating a known auto-thief, now in police custody, in the hopes he will be accepted by the hot-car ring working the city. He gets close before his identity is discovered and he is confronted at gunpoint by the gang-leader.