The butt of many a practical joke at the office where he works as a clerk, Joe Holt (Joe E. Brown) is nonetheless determined to prove himself a brilliant inventor. His latest creation is an unsinkable swim suit, which works quite well in theory. In practice, however, it is another matter; Joe can't test out the suit because he can't swim. As the result of a series of dizzying circumstances, Joe is mistaken for a swimming champ (Guinn "Big Boy" Williams) also named Joe Holt, and as such he makes the acquaintance of wealthy debutante Alice Brandon (Ginger Rogers). Through the auspices of Alice's father, "our" Joe is entered in the annual swimming marathon from Catalina Island to the California coastline. After taking a few "dry" swimming lessons from a youngster named Sam (Allan "Farina" Hoskins), the nervous Joe dives into the Catalina surf and starts the 22-mile swim. His unsinkable suit is a success, but there's many a slapstick obstacle placed in Joe's path before he can resurface at the finish line, thanks largely to the machinations of rival swimmer Edward Dover (Preston S. Foster).