A boxer named Tommy (Arthur Franz) barks up the wrong tree when he hires two inept private detectives (Bud Abbott, Lou Costello) to save him from a trumped up murder charge. Tommy has run afoul of the mob leader (Sheldon Leonard) who is fixing the matches. Fortunately for the boxer, he has a serum that can make him invisible, though it drives his two friendly investigators over the edge. They have trouble with the real police investigator (William Frawley) who tends to be a skeptic about invisible men. The boxer will fight his big bout while invisible, using Lou (Lou Costello) as the front man in the ring to hilarious effect.