Species: When a creature genetically engineered through extraterrestrial intelligence escapes from observation, scientist Xavier Fitch assembles an elite team of experts to track it down. The alien is traced to Los Angeles, and initiates a horrific plan, to mate with unsuspecting men and produce offspring that could destroy mankind.

Species II: An astronaut gets infected with alien DNA during the first mission on Mars and runs amok on earth. Preston and Laura team up with a peaceful, genetically re-engineered Sil to track the monster down.