A family of fitness freaks sets out to swim the English Channel.

On their small dairy farm in Arkansas, the health-conscious Higgins family begins each day with a vigorous swim in the lake. When Windy Webbe, promoter of a health tonic called Liquapep, comes to town with a traveling show, the family attends, and eldest daughter Katy fends off Windy's advances while her sister Suzie sings for the crowd. That night, Windy comes by to deliver a prize for Suzie's performance and resumes his attempts to court the indifferent Katy. When Windy learns that the entire family swam the fourteen-mile Winapoochet River the previous year, he senses a promotional opportunity and tries to convince the family to enter a contest to swim the English Channel, with Liquapep as their sponsor. Hoping to win enough money to buy a prize bull for their farm, Katy consents, and "The Liquapep Family" goes to England. As they look out across the Channel from Dover, the family is dismayed to learn that the actual swimming distance, taking the current into account, is not the twenty miles they expected, but at least thirty miles. One day, while training for the event, Katy is separated from Windy's boat by a thick fog, and instead swims to a rowboat manned by dashing Frenchman Andre Lanet. While Andre rows Katy to his yacht, Windy picks up vivacious French swimmer Gigi Mignon, who is immediately smitten with him. Andre tells Katy that he works for his family's champagne company, and transports their product across the Channel twice a week. Andre persuades Katy to dine with him that night, promising to tell her more about the Channel. The following day, Katy and Windy join Andre on his boat for lunch. While the seasick Windy is below deck, Andre declares his feelings for Katy, and they kiss. Feeling the need to devote more time to her training, however, Katy insists that they stop seeing each other. Several days later, the Higgins family moves on to France. The Channel swim is postponed because of bad weather, and Windy tells the family that only Katy will be allowed to compete. Pa takes the news badly, and when Katy tries to console him, he admits that he has gone heavily into debt to pay for improvements to the farm. That night, the troubled Katy dreams she is swimming the Channel with cartoon characters Tom and Jerry, as well as a French octopus that tries to keep her from completing the swim. In the morning, Ma convinces Katy to take the day off, and she visits Andre at his estate, where she becomes tipsy sampling the Liquapep. That evening, word comes that the Channel swim will begin the following morning. An exhausted Katy begins the swim in the pre-dawn darkness, with her mother and sisters following her in Andre's boat. Fourteen hours into the swim, Gigi grows too weak to continue, despite Katy's encouragement. Bad weather and rough waters plague the remaining swimmers, but Katy perseveres, and Andre jumps in and swims the last agonizing mile with her. Katy finishes the race and marries Andre, and Gigi becomes the new Liquapep girl.