While driving home from their summer vacation, siblings Paul and Marilyn find themselves stranded at a desolate truck-stop when their car breaks down along the back roads of upstate New York. Before long, they discover that a strange creature is being held in a cage behind the local auto shop, and the shop's mechanic, along with his assistant, plan on feeding them to it. In their attempt to escape, Paul and Marilyn fall prey to these two homicidal locals, bent on preserving the secret of their bloodthirsty pet monster.