Testing Einstein's Time Dilation Theory as a spaceship approaches the speed of light was the original purpose behind the centuries-long journey undertaken by Taylor (Charleston Heston) and his fellow three American astronauts. An accident of chance brought them to a future Earth where humanity had devolved into a primative state and where humans were hunted by intelligent Apes. The Ape Civilization believed that the only good intelligent human was a dead one and soon Taylor is in a race not only to save his own life, but to solve the riddle of the planet he had crash landed on.