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Producer/director Bert I. Gordon began his career-long devotion to movies about giant-sized people and animals with this low-budget chiller, which has a surprisingly strong cast of onetime Hollywood leading men. Gloria Talbott plays Susan Winter, a young American woman who hires soldier-of-fortune Russ Bradford James Craig to lead an expedition into a remote valley in Mexico where her fiance, Bruce Barton, was lost in a plane crash two years earlier. Also along are greedy speculator Martin Melville (Lon Chaney Jr.) and pilot Lee Brand (Tom Drake). They get to the valley and discover that it is, as was rumored, rich in deposits of uranium, but also dangerously radioactive -- the immediate threats include giant insects and spiders and huge mutated lizards, but Susan is positive that they're being watched by an unseen observer. The title creature, 25 feet tall with a disfigured face, a single eye, and motivated by the most bestial of impulses, shows himself by trapping them inside of a cave, and quicker than you can say Polyphemus, the rescue mission becomes a fight for survival that has a particularly nasty, bitter ending.