In space, officer Ellen Ripley and the cat Jones drift in a rescue capsule. They are the only two survivors of the Nostromo's tragedy, commercial freighter whose crew was decimated by a bloody monster, during its return on Earth.
Arriving near the Earth, the capsule is noticed by a small space shuttle that boads it and returns Ripley and Jones, always in suspended animation, towards station 'Gateway' to be nursed. When she wakes up, Ripley learns that she has wandered for more than 50 years in hibernation. Henceforth, nothing more keeps her to the Earth.
Ripley testifies the fights of the Nostromo's crew against the monstrous Alien. But members of the commission of the company have pain to believe her. However, as we get no news from Acheron colonists... an expedition is decided. Ripley, tortured by horrible nightmares, finish to accept to return with the scientific counselor Burke, the androïde Bishop (to whoom Ripley has very few esteem following to what arrived to her with Ash, the android of the Nostromo) and a commando of Marine corps on Acheron.
When they arrive on the colony, a scary spectacle certifies of violent combats. The crew of Marine corps notice the place where all colonists are retained captive thanks to their transmitter implants. A rescue mission is launched to liberate colonists gathered by the Aliens. The Mission turns rapidly to a nightmare. Not only colonists are lost, because the Aliens have already invest their bodies, but the group of Marine corps is attacked, and wiped by many losses. The crew withdraws in a commandment room. There, they will discover Newt, a little fearful girl who has known remaining hidden and who is reassured by Ripley.
In spite of Burke's protestations for whoom vital interest is to communicate with the Aliens and to return one home, Ripley takes the commandment with corporal Hicks. The landing shuttle having been destroyed during the preceding attacks, Bishop is charged to remote pilot a new one from the mother vessel in orbit around the planet. The emergency of evacuation is greater than the colony risks to explode at any time because of a gas emanation not controlled. The crew has to push out then aliens attacks until the arrival of the shuttle.
The foreseeable attack arrives. Despite all precautions, Aliens invest the trenched camp, sowing death again. Hicks is injured, Newt is removed.
Bishop succeed to remote pilot the shuttle. Ripley deposits Hicks into, then, taking her courage with two hands and armed to teeth, she leaves to the research of Newt. She finaly finds her and frees her just in time before an alien's egg opens. Escaping, Ripley and Newt face accidentally the alien's queen...
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Ripley will exterminate all the eggs then will escape to join the shuttle in which Bishop and Hicks wait for her. The colony Acheron explodes. Bishop has been able to evacuate in time Ripley and Newt...
But the queen has climbed on board the shuttle. Dressing a robot of handling, Ripley delivers a ultimate combat to equal arms against the creature that finishes expelled into outer space. Only survivors, Ripley, Newt, Bishop and Hicks return to Earth, in suspended animation...