Abbott and Costello Meet the Invisible Man (1951)

Lou Francis and Bud Alexander have just graduated from a private detective school. Tommy Nelson, a middleweight boxer, comes to them with their first case. Tommy recently escaped from jail after being accused of murdering his manager, and asks the duo to accompany him on a visit to his fiancée, Helen Gray. He wants her uncle, Dr. Philip Gray, to inject him with a special serum which will render Tommy invisible, and hopes to use the newfound invisibility to investigate his manager’s murder and prove his innocence. Dr. Gray adamantly refuses, arguing that the serum is still unstable, recalling that the formula’s discoverer, Jack Griffin, was driven insane by the formula and did not become visible again until after he was killed. However, as the police arrive Tommy injects himself with it and successfully becomes invisible. Detective Roberts questions Dr. Gray and Helen while Bud and Lou search for Tommy.

Helen and Tommy convince Bud and Lou to help them seek the real killer, after Tommy explains that the motive for the murder occurred after he refused to “throw” a fight, knocking his opponent, Rocky Hanlon, out cold. Morgan, the promoter who fixed the fight, ordered Tommy’s manager beaten to death while framing Tommy for the crime.