Ellen Ripley has been in stasis for 57 years in an escape shuttle after destroying her ship, the Nostromo, to escape a lethal alien creature which slaughtered her crew. She is rescued and debriefed by her employers at the Weyland-Yutani Corporation, who are skeptical about her claim of alien eggs in a derelict ship on the exomoon LV-426,[a] since it is now the site of the terraforming colony Hadleys Hope. After contact is lost with the colony, Weyland-Yutani representative Carter Burke and Colonial Marine Lieutenant Gorman ask Ripley to accompany them to investigate. Still traumatized from her alien encounter, she agrees on the condition they exterminate the creatures. Ripley is introduced to the Colonial Marines and an android, Bishop, on the spaceship Sulaco.

A dropship delivers the expedition to the surface of LV-426, where they find the colony deserted. Makeshift barricades and battle signs are inside, but no bodies; two live alien facehuggers in containment tanks and a traumatized young girl nicknamed Newt are the sole survivors. The crew finds the colonists beneath the fusion-powered atmosphere processing station and head to their location, descending into corridors covered with alien secretions. At the center of the station, the marines find the cocooned colonists serving as incubators for the creatures' offspring. The marines kill an infant alien after it bursts from a colonist's chest, rousing multiple adult aliens who ambush the marines and kill or capture many of them. When the inexperienced Gorman panics, Ripley assumes command, takes control of their armored personnel carrier, and rams the nest to rescue Corporal Hicks and Privates Hudson and Vasquez. Hicks orders the dropship to recover the survivors, but a stowaway alien kills the pilots and it crashes into the station. The survivors barricade themselves inside the colony.

Ripley discovers Burke ordered the colonists to investigate the derelict spaceship containing the alien eggs, intending to profit by recovering them for biological weapon research. Before she can expose him, Bishop informs the group the dropship crash damaged the power-plant cooling system; it will soon explode, destroying the colony. He volunteers to reach the colony transmitter and remotely pilot the Sulaco's remaining dropship to the surface.

After falling asleep in the medical laboratory, Ripley and Newt awaken to find themselves trapped with the two released facehuggers. Ripley triggers a fire alarm to alert the marines, who rescue them and kill the creatures. She accuses Burke of releasing the facehuggers to impregnate her and Newt, allowing him to smuggle the embryos through Earth's quarantine. The power is suddenly cut, and aliens attack through the ceiling. In the ensuing firefight, the aliens kill Burke, subdue Hudson, and injure Hicks; Gorman and Vasquez sacrifice themselves to stall the horde. Newt is separated from Ripley and captured.

Ripley and Hicks reach Bishop in the second dropship, but she refuses to abandon Newt. The group travels to the processing station, allowing a heavily-armed Ripley to enter the hive and rescue Newt. Escaping, they encounter the alien queen in her egg chamber. When an egg begins to open, Ripley uses her weapon to destroy the eggs and the queen's ovipositor. Pursued by the enraged queen, Ripley and Newt join Bishop and Hicks on the dropship and escape moments before the station explodes consuming the colony in a nuclear blast.

On the Sulaco the group is ambushed by the queen, who stowed away in the dropship's landing gear. The queen tears Bishop in half and advances on Newt, but Ripley fights the creature with an exosuit cargo-loader and expels it through an airlock into space. Ripley, Newt, Hicks, and the critically-damaged Bishop enter hypersleep for their return trip to Earth.

https://en.wikipedia.org/wiki/Aliens_(film)
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