In deep space, the crew of the commercial starship Nostromo is awakened from their cryo-sleep capsules halfway through their journey home to investigate a distress call from an alien vessel. The terror begins when the crew encounters a nest of eggs inside the alien ship. An organism from inside an egg leaps out and attaches itself to one of the crew, causing him to fall into a coma.
After floating in space for 57 years, Lt. Ripley's (Sigourney Weaver) shuttle is found by a deep space salvage team. Upon arriving at LV-426, the marines find only one survivor, a nine year old girl named Newt (Carrie Henn). But even these battle-hardened marines with all the latest weaponry are no match for the hundreds of aliens that have invaded the colony.
After escaping with Newt and Hicks from the alien planet, Ripley crash lands on Fiorina 161, a prison planet and host to a correctional facility. Unfortunately, although Newt and Hicks do not survive the crash, a more unwelcome visitor does. The prison does not allow weapons of any kind, and with aid being a long time away, the prisoners must simply survive in any way they can.
Two hundred years after Lt. Ripley died, a group of scientists clone her, hoping to breed the ultimate weapon. But the new Ripley is full of surprises … as are the new aliens. Ripley must team with a band of smugglers to keep the creatures from reaching Earth.