When Michael's father loses his job, he buys a boat and convinces Michael and his mother to sail around the world. It's an ideal trip - even Michael's sheepdog can come along. It starts out as the perfect family adventure - until Michael is swept overboard. He's washed up on an island, where he struggles to survive. Then he discovers that he's not alone. His fellow-castaway, Kensuke, is wary of him. But when Michael's life is threatened, Kensuke slowly lets the boy into his world. The two develop a close understanding in this remote place, but the question of rescue continues to divide them.