Glenn Manning, "The Amazing Colossal Man," believed dead after falling from the Hoover Dam, reemerges in rural Mexico, brain damaged, disfigured, and very angry.

Lt. Col. Glenn Manning is inadvertently exposed to a plutonium bomb blast and although he sustains burns over 90% of his body, he survives. Then he begins to grow, but as he grows he starts losing his mind. By the time he stops he is 50 ft tall, insane and is on the rampage.

Aliens equipped with venomous claws invade a small town, but the town's teenage population is mobilized to fight the menace.