In the near future, during its return to the earth, a commercial spaceship Nostromo intercepts a distress SOS from a distant planet. The seven-member crew are woken up from the hypersleep and the spaceship subsequently descends on the planet. While exploring the planet, a three-member team of the crew discovers a derelict spaceship and a huge chamber inside it containing thousands of eggs. When a curious team member goes too near the egg the parasite inside the egg attacks him, rendering him unconscious. He is brought back aboard, the spaceship takes off. After a little while the parasite dies and his host wakes up seemingly unruffled. But other crew members are unaware of the living nightmare which is going to descend upon them when the alien creature planted inside its unfortunate host would emerge.