Taking a page from Ridley Scott's groundbreaking sci-fi classic Alien, this little-seen space thriller centers on the doomed mission of a group of space explorers sent to investigate the caverns of a distant planet. When the beautiful Sandy (Judy Geeson) is attacked and impregnated by a menacing alien, the gestating offspring turn her into a homicidal monster and she begins to pick off her fellow crew members in bloody fashion, one by one.