While returning from a space mission, Nostromo is awakened by a supposed SOS call from a system they are passing through. Descending to the planet's surface, they discover a strange spaceship. What he finds are thousands of strange alien eggs. While examining one of the eggs, it hatches and attacks him. After returning to the Nostromo the crew takes off again to head for Earth. The alien parasite died and all seems well again. But what no one knows is that another alien is forming within its host and when it emerges, the crew finds itself in serious trouble.