Plot

A group of scientists try to track down and trap a killer alien seductress before she successfully mates with a human.

In 1993, a search for extraterrestrial life, a transmission's received, detailing an alien DNA structure, along with instructions on how to splice it with human DNA. The result is Sil, a sensual but deadly creature who can change from a beautiful woman to an armor-plated killing machine in the blink of an eye. Government agent Xavier Fitch assembles a team of scientists and mercenaries to locate and destroy Sil before she manages to find a mate and breed.—Amazon

A group of scientists try to track down and stop a killer alien. In 1974, the United States government relayed a message containing information about Earth and its inhabitants (including the DNA sequences which make up the human genoome) out to the galaxy. But now, 20 years later, a reply arrives; it contains a unique sequence of DNA, along with instructions of how to combine it with their own. An experiment's undertaken and within weeks, one of the injected human ova grows into a seemingly normal female child, called "Sil." It soon becomes apparent she possesses dangerous alien characteristics. She's part human, part alien, strong, dangerous and desperate to mate with a human.—Anthony Pereyra {hypersonic91@yahoo.com}

A message is sent out to space to whatever intelligent life form out there might be listening. Approximately 20 years later, a reply is received; it gives the scientists information of an alien species' DNA structure and instructions on how to mix their DNA with human DNA. The science team successfully creates a hybrid,which they codename Sil. Due to some mistakes, the experiment had to be stopped. Sil manages to escape, murdering people. She is on a mission to mate with a human male, but the team gathered has to quickly catch her and stop her. If Sil manages to mate, she'd produce offspring which will destroy Earth.—Kellye Boyd

The alien is the result of the SETI (Search for Extra Terrestrial Intelligence) program. In 1974 Earth's scientists sent out transmissions with information about Earth and its inhabitants, DNA structure, etc., in hopes of finding life beyond Earth. Twenty years later, they receive two transmissions from an alien source. The first transmission was on how to create endless fuel effortlessly through a methane catalyst. Therefore, the scientists assume that this is a friendly alien species.

But from a second alien transmission, the scientists receive information about an alien DNA sequence along with instructions on how to splice it with human DNA. A government team led by Xavier Fitch (Ben Kingsley) goes forward with the genetic experiment, hoping to induce a female with "more docile and controllable" traits. One of the one-hundred experimental ova produces a girl named Sil, who looks like a normal human but develops into a 12-year-old in three months.

Sil's violent outbursts during her sleep make the scientists consider her a threat. They try to kill her using cyanide gas, but instead she breaks out of her containment cell and escapes out into the world. The government assembles a team composed of anthropologist Dr. Steven Arden (Alfred Molina), molecular biologist Dr. Laura Baker (Marg Helgenberger), empath Dan Smithson (Forest Whitaker) and mercenary Preston "Press" Lennox (Michael Madsen) to track and destroy Sil.

While sleeping, Sil has another dream of an alien train running her down. When she wakes up, tentacles start emerging from underneath her skin and mass to form an organic cocoon around her.

While transforming within the cocoon, Sil kills a train warden before emerging as a blonde, twenty-something adult woman. Also, when Sil emerges she is naked, the reason for which is unknown. It can be assumed that the cocoon that enveloped her destroyed her clothes but it can also be assumed that she removed them during the process, though if the latter is correct it is unclear why.

Sil waits in the train until it has arrived at Los Angeles. This makes tracking her extremely difficult.

She is incredibly strong and intelligent with amazing regenerative powers. The scientists fear she may seduce someone to copulate with her in order to reproduce and any offspring could eventually exterminate mankind. Sil lacks inhibitions when it comes to harming or even killing people who get in her way and wants to reproduce as soon as possible.

She tries first to mate with a man she meets at a night club, but she rejects and kills him after sensing he is diabetic. She then tries to mate with a man she meets after a car accident, this is interrupted by Press and Laura. While attempting to keep him from alerting them, she rapidly transforms into her natural form (a bipedal, humanoid creature with silted pupils, no hair, dark/colored skin and a pair of flexible tentacles both of which she keeps stored inside one of her breasts and can retract at will) and attempts to restrain him with her tentacles, forcing one of the tentacles into his mouth to keep him from screaming; inadvertently killing him.

Sil then flees into the forest without being seen by the team but does not have enough time to retrieve her clothes, forcing her to flee naked.

After cutting and dying her hair, she takes an attraction to Press. She eventually partially disrobes to seduce Arden. This succeeds and she and Arden remove the rest of their clothes before she copulates with him, becoming impregnated.

Sil then quickly kills Arden when he realizes who she is and flees naked into the sewers where she gives birth to her son.

The rest of the team follows her. Sil kills Fitch. Dan lights Sil's son on fire; the son then falls into the pool of oil, killing him. Enraged, Sil attacks Press but he shoots her into the burning pool, where she grabs onto Dan's leg. Press shoots Sil with his grenade launcher, instantly killing her.

The last scene shows a rat chewing on one of Sil's severed tentacles; it mutates a long tongue and attacks another rat with it.