A broke inventor of a non-sinkable bathing suit is mistaken for a champion swimmer by an attractive woman in this far-fetched comedy.
At a rubber company Harry Daniels (Harry Gribbon) and other employees send a letter from president Armstrong, asking Joe Holt (Joe E. Brown) to demonstrate his non-sinkable bathing suit; but Armstrong sends Joe back to the shipping room, as the employees laugh. An attorney tells Joe he has inherited his Aunt Minnie's estate in California. On the way out Joe gives Harry a kick.
In California a lawyer tells Joe he must take care of Sam (Allen 'Farina' Hoskins), a black boy. Expecting a million, Joe gets worthless stocks and $5.80. Joe and Sam sleep in a park. Alice Brandon (Ginger Rogers) pages Joe Holt and tells him he is going to stay with her father at Catalina. When the swimmer Joe Holt arrives, he finds no tickets and is arrested for fighting with the police. The boat arrives at Catalina, and Tom Brandon (Walter Walker) welcomes "champion" Joe Holt, who also meets aqua-planer Ed Dover (Preston Foster). Brandon expects Joe to swim in the 21-mile race to the mainland. The police call Brandon, who tells them their Joe Holt is an impostor.
Sam reminds Joe he is broke. Alice asks Jim to beat Ed in the race. He thinks he should confess; but he promises, and Alice kisses him. Joe tries to learn how to swim with Sam's help. Ed takes Joe aqua-planing and falls out of the boat. Alice thinks that Joe rescued Ed. Joe says his back hurts in order to get out of the race. Alice takes care of Joe. Believing the race has started, Joe says he's cured; but Dr. Vorse got the race postponed. Harry brings the non-sinkable suit. Joe pleads to use it; but Harry expects Joe to drown. However, Sam got the suit, and Joe tries it. Alice replaces the suit. Sam prays to help Joe.
The swimmers put on oil. Joe goes back to kiss Alice. Joe sinks to the bottom but manages to flounder on. After five hours he gets pulled by a line. Then Alice tells Joe she gave him the suit, and he sinks again. When she tells him that suit is also non-sinkable, Joe catches Ed, who threatens to drown him. Joe swims under Ed to take the lead. Joe gets caught in seaweed but pops up to win, wearing seaweed; then he collapses. In the final scene Joe dives into a pool with Alice, who tells him his suit is not non-sinkable. Joe sinks again.
This spoof of marathon swimming uses the fantasy of an invention and the psychology of whether one believes it is true or not.