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 Stella 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, an elderly Japanese man named Kensuke, has lived on the island since the bombing of his native Nagasaki. Kensuke keeps his distance at first, 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.