Decades after his entire tribe was slaughtered, the sole survivor of the attack, Ishi, (Graham Greene) comes out of hiding having lived for years in isolation. Anthropologist Alfred Kroeber (Jon Voight) learns of Ishi's story and makes it his subject of study. Impressed with the man's courage and eager to learn the tribe's history, Kroeber takes Ishi in and devotes his research to finding out the truth.