A young boy and his family set off on a sailing trip of a lifetime. Excitement turns to terror when a violent storm erupts and Michael and his dog, Stella, are swept overboard. They are washed up on to a remote island, terrified and struggling to survive. 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 Two, 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.