Having just returned from a mission to Mars, Commander Ross isn't exactly himself. He's slowly becoming a terrifying alien entity with one goal -- 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 Eve, a more tempered alien clone, to find Ross and his brood. Before long Eve escapes to mate with Ross.

After she delivers her child in an ambulance, alien Eve is killed by a half-breed. Fortunately, Dr. Abbot scoops up the baby alien and escapes. In time, the baby grows into a gorgeous blonde named Sara and begins her quest to find a worthy mate. But Sara is also savage and leaves a trail of deaths in her wake. This carnage makes chemistry student Dean question whether to help her race or not.