When Ellen Ripley finally returns to Earth, she learns that the planet LV-426 - now called Acheron - has been colonized. But LV-426 is where Ripley and the crew of the Nostromo found the original Xenomorph - the killing machine known as the Alien. Protected by the Colonial Marines, the colonists seek to terraform the storm-swept planet.

Two such residents are Anne and Russell Jorden, seeking a fortune that eluded them on Earth. On Acheron, Anne gives birth to the colony's first newborn. Rebecca Jorden, also known as Newt.

The wildcatters discover a vast, decaying spaceship. The horseshoe-shaped vessel is of particular interest to Weyland-Yutani, and may be the answer to their dreams. But what Anne and Russ find on board proves to be the stuff, not of dreams, but of nightmares.