A young boy, Michael, and his family set off on a sailing trip of a lifetime. However, excitement turns to terror when a violent storm breaks out, resulting in Michael and his dog Stella being washed overboard into the vastness of the Indian Ocean. Barely alive, they are stranded on a remote island. Michael is terrified and struggling to survive until he wakes up one morning to find some fish and coconut milk left next to him. He realizes he is not alone, but who else is on the island?

As he hears a plane overhead, Michael rushes to build a fire to attract attention, but he is horrified when the fire is ruthlessly extinguished by another person, a mysterious Japanese man named Kensuke who has chosen to live alone on the island since World War Two. Michael learns that Kensuke has created an extraordinary bond with the island and its inhabitants – a group of orangutans. However, one day the orangutans are threatened by the explosive arrival of illegal poachers. Michael finds resources he never knew he had and Kensuke learns to abandon his distrust of humanity as they join forces to protect and nurture their secret world.