In 1974, the United States government relayed a message containing information about Earth and its inhabitants--including the DNA sequences that make up the human cell--to the rest of the galaxy. Twenty years later, a reply finally arrives, containing a unique sequence of DNA--along with the friendly instruction to combine it with our own. A top secret experiment is undertaken and within weeks one of the injected human ova grows into a seemingly normal female child, called "Sil." It soon becomes apparent, however, that she possesses dangerous alien characteristics. The decision to exterminate the "child" meets with disastrous results when the rapidly-developing Sil escapes into the desert. A specialized team is quickly assembled to locate Sil, but what they don't realize is that their quarry has metamorphosed into what appears to be a stunningly beautiful young woman who's loose in Los Angeles with a relentless inner drive to mate with a human being.