The film takes place in New Zealand in 1868 during Titokowaru's War between the Māori people and New Zealand colonial forces. Sarah O'Brien (Samantha Morton) has grown up among soldiers in a frontier garrison on Te Awa Nui, the Great River. Pregnant at 16 by a young Maori boy, she gives birth to a son. When, 7 years later, her son, Boy, is kidnapped by his Maori grandfather, Sarah is distraught.