In 1974, an organization known as the Search of ExtraTerrestrial Instituion (SETI) has possessed some kind of alien being, thus beginning some kind of top secret experiment to mix human and alien DNA. This is when the scientists created Sil, a female human-alien hybrid. However, approximately 20 years later, she has escaped. Sil is also determined to reproduce, but needs human male sperm to do so. Now, a team of scientists and federal agents must find Sil and stop her from mating with a human male and reproduce.