The Rugrats embark on a relaxing family "cruise," only to have a storm sink their boat! They find themselves marooned on an island with no phone, radio, or...diapers! The adults, thinking they're on a deserted island, try to find a way to survive. Meanwhile Tommy Pickles and the other babies run into the Thornberrys! Tommy is sure that his hero, Nigel Thornberry, can help them get off the island. But when Nigel bumps his head and is knocked out, he wakes up speaking baby talk! To make matters worse the babies get stuck underwater in the Thornberrys' bathysphere. With air running out, the babies find themselves in a race against time. Will they be able to get out before it's too late?