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.

Ellen Ripley is sent back to the planet LV-426 to establish contact with a terraforming colony. Once there, she encounters the Alien Queen and her offspring and has to fight them to survive.