Milquetoast Henry Limpet experiences his fondest wish and is transformed into a fish. As a talking fish he assists the US Navy in hunting German submarines during World War II.
Set in Prohibition era Chicago, bootlegger Robbo and his cronies refuse to pay the greedy Guy Gisborne a cut of their profits after Guy shoots mob boss Big Jim and takes over. When Big Jim's daughter, Marian, gives Robbo a large sum, believing he has avenged her father's death, the gangster donates to an orphanage, cementing his reputation as a softhearted hood.
While diving for sunken treasure, street-smart gumshoe Tony Rome finds the body of a gorgeous blonde, her feet stuck in a block of cement. Soon after, tough guy Waldo Gronski hires him to find a missing woman named Sandra Lomax, and Rome wonders if there's a connection. He sets about trying to locate the woman, and in no time finds himself mixed up with a beautiful party girl and a slippery racketeer.
