Man has split the atom and created the ultimate weapon. But how could he have known he would also create Them!? The terror begins when a hard-nosed patrolman (James Whitmore) discovers a dazed child wandering in the New Mexico desert near a car and house trailer destroyed by a mysterious force. Whitmore next discovers a ransacked general store; its cash drawers are full but the sugar supply is missing. And on the floor lies a battered corpse containing...

A cowboy captures a prehistoric beast and hits on the idea of putting it on display at a traveling circus. The beast, however, has other ideas.