A young boy and his family set off on a sailing trip of a lifetime until a violent storm erupts, sweeping Michael and his dog overboard. After washing up on a remote island, terrified, they struggle to survive and adjust to life alone, One day, Michael discovers he is not alone when he is confronted by a mysterious Japanese man who has lived there secretly since World War II, angry that Michael has arrived. However, as dangerous invaders threaten their fragile island paradise, Michael and the old man, Kensuke, join forces to save their secret world.