A commercial spaceship, the Nostromo, on its return journey to Earth, intercepts a distress signal from a nearby planetoid. The crew is awakened from cryosleep by the ship's computer to investigate, as their company policy requires potential salvage opportunities be explored. Upon landing, the ship suffers some damage, and while repairs are being made, the captain authorizes a small team to track the signal's source. They discover a derelict alien spacecraft which houses a chamber containing numerous egg-like objects. While inspecting one of these, a crew member is attacked by a creature that springs from the egg and attaches itself to his face.

Upon returning to the Nostromo, debates arise about quarantine procedures but ultimately the crew enters with the unconscious member. The creature attached to his face seemingly dies and detaches after a period, allowing the crew to believe the danger is over. However, they soon discover that is far from the truth when a new creature emerges, threatening the lives of everyone on board. The crew must now navigate the dual perils of retaining their own survival while confronting a mysterious and lethal alien organism, which proves to be a formidable and elusive adversary within the confines of their spaceship.