A surfer by the name of Duke Williams washes up on the shore and collapses, having spent five days at sea on his surfboard. The girls fall for Duke, played by Denny Miller, so Gilligan tries to learn how to surf by tying his feet to Duke's surfboard. Despite their interest in the newcomer, Ginger and Mary Ann panic when he makes a pass at each of them. To resolve the conflict, the castaways pretend the girls are not available. Ginger is with the Professor and Mary Ann is with Gilligan. So, Duke decides to leave the island and manages to depart by catching a huge wave. The men sit around the radio, anxiously listening to news of Duke's arrival in Hawaii. To their dismay, Duke doesn't remember where he's been for the last two weeks, having hit a rock and suffered amnesia.