A Kentucky woman, Dian Fossey is inspired by anthropologist Louis Leakey to devote her life to the study of primates. Travelling into deepest Africa, Fossey becomes fascinated with the lives and habits of the rare mountain gorillas of the Rwandan jungle. Studying them at close quarters, Fossey develops a means of communicating with the gorillas, and in doing so becomes obsessed with the apes' well-being. She becomes so preoccupied with her vocation that she loses the opportunity of a romance with the National Geographic photographer Bob Campbell.
Appalled by the poaching of the gorillas for their skins, hands, and heads, Fossey complains to the Rwandan government, which dismisses her, claiming that poaching is the only means by which some of the Rwandan natives can themselves survive. She rejects this, and dedicates herself to saving the African Mountain gorilla from illegal poaching and likely extinction. To this end she forms and leads numerous anti-poaching patrols, and even burns down the poachers' villages and stages a mock execution of one of the offenders.
Fossey is mysteriously murdered on December 26, 1985, in the bedroom of her cabin.