Based on the novel by Theodore Pratt, this quaint little children's fantasy leads the viewer on a deep-sea adventure. Henry Limpet (Don Knotts), a bespectacled, milquetoast bookkeeper, loves his pet fish so much that he longs to be one. When Henry's wish comes true and he's turned into a talking fish, the simple ocean life he'd envisioned proves more exciting than mundane as he helps the U.S. Navy defeat the Nazis during World War II!