Recent detective school graduates Bud and Lou are minding their new business when accused killer Tommy Nelson bursts into their office. Proclaiming his innocence, he convinces the two to get him to his beautiful fiancée Helen. Just as the police arrive to investigate, Tommy injects himself with invisibility serum being developed by Helen's uncle. Tommy convinces Lou to go undercover as a boxer to help expose the real killer. With Tommy's unseen assistance, Lou reluctantly goes into the ring as "Lou the Looper" for one of the most hilarious fight sequences ever filmed. © 1951 Universal Studios. All Rights Reserved.