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.
In the distant future, the crew of the commercial spaceship Nostromo are on their way home when they pick up a distress call from a distant moon. The crew are under obligation to investigate and the spaceship descends on the moon afterwards. After a rough landing, three crew members leave the spaceship to explore the area on the moon. At the same time as they discover a hive colony of some unknown creature, the ship's computer deciphers the message to be a warning, not a distress call. When one of the eggs is disturbed, the crew realizes that they are not alone on the spaceship and they must deal with the consequences.