In the distant future, the commercial spaceship "Nostromo" crew is on its way home when the crew picks up a distress call from a distant moon. The crew must investigate, and the spaceship descends on the small planetoid afterwards. After a rough landing, three crew members leave the spaceship to explore the area on the planetoid. At the same time, the ship's computer deciphers the message. When the crew realizes it is not alone on the spaceship, they must deal with the consequences.