Francis, the Famous Talking Mule

Francis and Pete spend the night in a farmer's barn. During the night a flash flood washes the barn down the river and out into the ocean. They wash up on a tropical island, inhabited by a hermit named Robinson Crewcut. The hermit has a cave full of diamonds that had washed up on the beach. Francis and Pete take a handkerchief full of diamonds and then capture the captain of a ship of smugglers. Pete impersonates the captain and tricks the crew into taking them back to the United States.