For thirty years, powerful telescopes have been scanning the space searching from signal of alien civilization. In 1974, the SETI (Search for Extra Terrestrial Intelligence) team sends a message to the space with the human DNA, map of our solar system and other information. In return, they receive two messages: the first one, with a catalyst for methane; the second, a detailed alien DNA together with instructions to join it with human DNA. The result of the experiment is the deadly creature Sil. When Dr. Xavier Fitch, who is leading the research, decides to terminate the experiment, the girl Sil escapes to Los Angeles. Dr. Fitch joins the mercenary Preston Lennox; the anthropologist Dr. Stephen Arden; the scientist Dr. Laura Baker; and the empathic Dan Smithson to chase Sil. Sooner they discover that the predator Sil has grown-up and became a beautiful woman, trying to copulate to generate an offspring.