Ellen Ripley, portrayed by Sigourney Weaver, is miraculously rescued after spending 57 long years in stasis, drifting through the void of space. Upon her return, she faces a rigorous debriefing from the Weyland-Yutani Corporation regarding the shocking destruction of her ship, the Nostromo. Skepticism clouds her testimony as the corporation questions her harrowing account of an Alien creature that resulted in the demise of her crew. Determined to convey the truth, Ripley underscores the threat the Alien posed; although she succeeded in eliminating it, she warns that the alien vessel harbored thousands of eggs. Should any find their way to Earth, the consequences could be catastrophic as these creatures gestate within living hosts.
Now located in Zeta Reticuli, the Exomoon LV-426 has transformed into a Terraforming colony named Hadley's Hope, where about 60 to 70 families have labored for over two decades to create a breathable atmosphere. Tragically, one of the exploratory teams stumbles upon the derelict alien ship, inadvertently triggering a breeding cycle when an egg hatches, leading to disaster as it attaches itself to one of the explorers.
As communication with Hadley's Hope abruptly ceases, Weyland-Yutani sends representative Carter Burke (played by Paul Reiser) and Colonel Marine Lieutenant Gorman (William Hope) to enlist Ripley's help in investigating the dire situation. Although haunted by her previous encounter with the Alien, Ripley initially hesitates to join them. However, after grappling with recurring nightmares about the creature, she agrees, provided Burke assures her that the priority will be extermination, not capture.
Aboard the USS Sulaco, Ripley meets the Colonial Marines and the android Bishop (Lance Henriksen), filling her with unease due to her previous traumatic experience with the treacherous android Ash. Upon landing on LV-426, the team discovers the facilities vacated. Signs of struggle are evident, but the colony is eerily empty except for two live face-Huggers contained within a medical lab and one survivor—a young girl nicknamed Newt (Carrie Henn) who narrowly escaped death by hiding in the ventilation system.
Using the colony's advanced computer systems, the team manages to detect the missing colonists sheltered beneath the power station. As they navigate the station's dark, secreted corridors, they shockingly uncover colonists cocooned, serving as hosts for Alien offspring. Their mission spirals into chaos when an encounter with a newborn Alien leads to an ambush that results in multiple casualties among the marines.
In a critical moment, panic-stricken Gorman falters, prompting Ripley to assert command, steering their vehicle with dire urgency as they crash through the nest to rescue her fellow marines—Hicks (Michael Biehn), Hudson (Bill Paxton), and Vasquez (Jenette Goldstein). However, disaster strikes when the crew's drop-ship is brought down by a hidden Alien, forcing Ripley, Newt, Burke, and the surviving marines to seek refuge inside the colony.
Ripley soon uncovers a terrifying plot: Burke had orchestrated the colonists' visit to the derelict ship, driven by greed and the ambition to exploit Alien specimens for bioweapons. Threatened by her knowledge, Burke’s ulterior motives push Ripley to act. Amidst this betrayal, Bishop reveals an even graver danger: the power plant has sustained serious damage during their conflict and is on the brink of catastrophic detonation.
As Ripley and Newt find momentary safety in the medical lab, their brief respite ends as two face-Huggers are released, prompting a desperate alert to the marines. With the Marines’ timely intervention, they manage to eliminate the face-Huggers. Ripley soon confronts Burke over his ruthless intentions to sacrifice her and Newt, aiming to facilitate his sinister escape plan. The confrontation escalates as Aliens begin an all-out assault, leading to the loss of more lives.
In a race against time, Ripley, horrifically aware of the danger Newt faces, assembles a makeshift weapon and valiantly descends into the depths of the processing station to rescue her from the clutches of the Alien queen. A fierce battle ensues as Ripley destroys the alien eggs, inciting the wrath of the queen who breaks free from her lair, pursuing them with deadly intent. Time is of the essence as they meet Bishop and Hicks, narrowly escaping moments before the colony is obliterated.
Yet the nightmare isn't over; aboard the Sulaco, they soon discover that the Alien queen has stowed away. In a horrifying twist of fate, she attacks Bishop, dismembering him in her rampage toward Newt. With determination, Ripley engages in an epic showdown against the queen using a powerful Exosuit, ultimately evicting the creature into the void of space. As the survivors—Ripley, Newt, Hicks, and the injured Bishop—enter hyper-sleep for their journey back to Earth, they can finally hope for peace, but the specter of the Alien remains, lurking in memory.
