During its return to the earth, commercial spaceship Nostromo intercepts a distress signal from a distant planet. When a three-member team of the crew discovers a chamber containing thousands of eggs on the planet, a creature inside one of the eggs attacks an explorer. The entire crew is unaware of the impending nightmare set to descend upon them when the alien parasite planted inside its unfortunate host is birthed.

Ripley, the sole survivor of the Nostromo's deadly encounter with the monstrous Alien, returns to Earth after drifting through space in hypersleep for 57 years. Although her story is initially met with skepticism, she agrees to accompany a team of Colonial Marines back to LV-426.

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.