Plot

After investigating a mysterious transmission of unknown origin, the crew of a commercial spacecraft encounters a deadly lifeform.

In the distant future, the commercial spaceship "Nostromo" crew is on its way home when the crew picks up a distress call from a distant moon. The crew must investigate, and the spaceship descends on the small planetoid afterwards. After a rough landing, three crew members leave the spaceship to explore the area on the planetoid. At the same time, the ship's computer deciphers the message. When the crew realizes it is not alone on the spaceship, they must deal with the consequences.—blazesnakes9

In cold, boundless space, AI super-computer Mother picks up a distress signal from Acheron, a barren nearby moon. Bound by protocol, it awakens the 7-member crew of the commercial towing vehicle, USCSS Nostromo, from cryosleep. Soon, as Captain Arthur Dallas and his crew descend to the inhospitable celestial body known as LV-426 to investigate the mysterious transmission, they discover a downed extraterrestrial spacecraft and its bizarre cargo. Now, dark questions loom. Was the cryptic signal a desperate SOS or a warning? Either way, something else has somehow found its way into the Nostromo, and its silent corridors will never be safe again. Who can confront the Alien, the unwanted eighth passenger?—Nick Riganas

In the distant future, the crew of the commercial spaceship "Nostromo" are returning home, when they receive a distress signal from a remote moon, located somewhere in the Zeta Reticuli quadrant. As per company policy, the large towing vessel makes a landing to investigate closer. Three of the crew set out to explore the area and discover a hive colony of unknown origin - just as the ship's computer deciphers the message to be a forewarning, in stead of a distress call. And when one of the eggs is disturbed from its dark and hideous slumber, the crew eventually realize that they aren't alone anymore. And a dire struggle for survival ensues.

The commercial towing spaceship Nostromo is on a return trip from Thedus to Earth, hauling a refinery and twenty million tons of mineral ore, and carrying its seven-member crew in stasis. Upon receiving a transmission of unknown origin from a nearby Planetoid, the ship's computer, Mother (Helen Horton), awakens the crew. The crew was returning with a full load of the ore and expected a large bonus upon arrival at Earth. The crew still believes that they have been awakened as they are nearing their destination but get a rude jolt when they realize that they are not in the Solar System. Mother summons Ship captain Dallas for a private conversation and apprises him of the situation. Dallas informs the crew that they are only halfway to Earth. Dallas says that the signal that Mother intercepted was acoustical beacon which repeats at an interval of 12 seconds.

Following company policy (and a clause in everyone's contract) to investigate transmissions indicating intelligent life, they land on the planet. The crew does not have any choice as if they fail to comply it results in complete forfeiture of shares, which means that the crew gets no money.

The crew detaches the Nostromo from the refinery and lands on the Planetoid, resulting in some damage to the ship due to the planet's jagged terrain. Captain Dallas (Tom Skerritt), Executive Officer Kane (John Hurt), and Navigator Lambert (Veronica Cartwright) the Nostromo's navigator, set out to investigate the signal's source while Warrant Officer Ripley (Sigourney Weaver) the warrant officer, Science Officer Ash (Ian Holm), and Engineers Brett (Harry Dean Stanton) and Parker (Yaphet Kotto) stay behind to monitor their progress and make repairs. Parker says that it will take 25 hours to repair the ship. The atmosphere of the planet is almost primordial which high concentrations of methane and Carbon-Dioxide. The planet is hostile with high winds and flying debris, which drops the visibility down to only a few feet.

Dallas, Kane, and Lambert discover that the signal is coming from a derelict alien spacecraft which is shaped like a horseshoe. The spaceship itself is huge with advanced equipment, well beyond the capabilities of humans. Inside it they find the remains of a large alien creature whose ribs appear to have been exploded outward from the inside. Meanwhile, the Nostromo's computer, Mother, partially deciphers the signal transmission, which Ripley determines to be some type of warning. The spaceship is very hot inside, even though the ship has been dead for a very long time (even centuries) as the alien creature found dead had been fossilized.

Kane discovers a vast chamber containing numerous eggs. The eggs are covered with a thin layer of mist and are activated when the mist is removed. Kane can see that there is organic life inside the egg. When he touches one of the eggs, a spider-like creature springs out, penetrates his helmet, and attaches itself to his face. Dallas and Lambert carry the unconscious Kane back to the Nostromo. As the acting senior officer, Ripley refuses to let them aboard, citing quarantine regulations (which requires 24 hours of mandatory decontamination), but Ash overrides her and allows the crew back into the ship.

While Parker and Brett work on repairing the Nostromo, Ash attempts to remove the creature from Kane's face. When Ash tries to pull one of the creature's digits, it tightens its tail around Kane's neck, strangling him. He stops when he discovers that its highly corrosive acidic blood could harm Kane and potentially damage the ship's hull. A small trickle of the creature's blood which dripped from a small incision was able to eat through 3 layers of decks on the ship. Eventually the creature detaches on its own and is found dead. With the ship repaired, the crew resume their trip back to Earth.

Kane awakens seemingly unharmed, but during a meal before re-entering stasis he begins to choke and convulse until an alien creature bursts from his chest, killing him and escaping into the ship. Lacking conventional weapons, the crew attempt to locate and capture the creature by fashioning motion trackers, electric prods, and flamethrowers.

Brett follows the crew's cat into a large room where the now-fully-grown Alien (Bolaji Badejo) attacks him and disappears with his body into the ship's air shafts. Dallas enters the ducts with a flamethrower, intending to force the creature into an airlock, but it attacks him. Parker later finds only the flamethrower.

Lambert implores the remaining crew members to escape in the ship's shuttle, but Ripley, now in command, explains that the shuttle will not support four people and insists on continuing Dallas's plan to flush out the alien.

While accessing Mother, Ripley discovers that the crew was awoken and directed to the planet because the company secretly ordered Ash to return with the alien for study, and to consider the crew expendable. She confronts Ash, who tries to kill her. Parker intervenes, knocking Ash's head loose and revealing him to be an android. The survivors reactivate Ash's head, and he confirms the company's orders. Ash states that the alien is not easily killed and expresses his admiration for it, taunting them about their chances of survival. Ripley shuts him down and Parker incinerates him.

The crew decides to self-destruct the Nostromo and escape in the shuttle. While gathering supplies, Parker and Lambert are killed by the alien. Now alone, Ripley initiates the self-destruct sequence, but the alien blocks her path to the shuttle. She retreats and unsuccessfully attempts to abort the self-destruct. She reaches the shuttle unhindered with Jones, narrowly escaping as the Nostromo explodes.

As Ripley prepares for stasis, she discovers the alien has stowed itself in a narrow compartment. She dons a spacesuit and flushes it out. It approaches Ripley, but before it can kill her, she opens the airlock door. The resulting explosive decompression almost ejects the alien into space, but it hangs onto the door frame. Ripley fires a grappling hook gun to push it out and activates the engines, blasting the alien into space. After recording her final log entry, she places Jones and herself into stasis for the trip back to Earth.