Young psychiatric resident Theo Caulder (Cuba Gooding Jr) is chosen to evaluate the mental competence of anthropologist Ethan Powell (Anthony Hopkins), determining whether he is fit to stand trial for murder. Powell has been extradited from Rwanda where he was captured by the authorities after killing members of a search party sent to locate him. It emerges that after years spent among the gorillas, Powell has adopted an ape-like mindset and rejected accepted human morality. Caulder soon realises that Powell is every bit his intellectual equal, and that exploring the anthropologist's mind may take him into increasingly dangerous territory.