Just back from Mars, Commander Ross is slowly becoming an alien entity with a one track mind--to procreate with human women! When countless women suffer gruesome deaths after bearing half-alien offspring, scientist Laura Baker and hired assassin Press Lennox use the beautiful Eve, a more tempered alien clone, to find Ross and his virulent brood. But they underestimate Eve's maternal drive, and before long she escapes to mate with Ross and create an unstoppable race that will destroy mankind.