Rising young boxing star Gene Harris (Nugent) is sent to prison after one of his opponents dies in the ring. Gene is paroled to a fight promoter who advertises him as "Killer" Harris, and is aided his schemes by Gene's fiancee, the wicked Claire (Lund), and a crooked fight manager. The trio plot to have Gene kill all his opponents so they can get rich quick from all the publicity. Added to the mix are subplots involving Mary (Barclay), the promoter's secretary, who has fallen in love with Gene, but who doesn't notice her due to Claire's evil charms. Also, Gene's dog nearly steals the show in constantly interrupting Gene from dunking his donuts, and later becoming a dog detective helping Mary and Gene get to the bottom of the criminal plots against him.