A crawl after the opening credits explains that in the near future, the technology that created synthetic humans enters a new phase: replicants, sophisticated androids that are virtually identical to humans, are now equal in strength and emotion to their creators. Replicants are designed and built by the Tyrell Corporation, a giant multiconglomerate headquartered in two pyramid-like towers. The latest version of replicant technology is the Nexus 6 model. Replicants are mostly used as manual laborers in the "off world" colonies out in space. Because of their advanced nature and tendency towards violence, replicants have been outlawed on Earth. Specialized police units, "blade runners," are charged with the difficult task of detecting replicants who come to Earth. If found, replicants are executed or "retired." An opening title sets the story in Los Angeles in November, 2019. LA and the surrounding area have become heavily industrialized, crowded with people, and rain falls constantly.
At the Tyrell Corporation, a blade runner, Holden (Morgan Paull
), is interviewing a new employee using a special device called a Voight-Kampff (VK) analyzer. The machine is designed to detect any physical changes in the test subject in response to questions that are deliberately meant to affect the subject emotionally. After a few questions, the man being tested, Leon Kowalski (Brion James
), becomes obviously agitated and eventually hostile, shooting Holden. (We learn later that Holden survived: "He can breathe okay, as long as nobody unplugs him.")
Rick Deckard (Harrison Ford
), a former blade runner, is eating at a Japanese noodle bar when another man, Gaff (Edward James Olmos
), tells him he's under arrest. Deckard tries to ignore the man but eventually agrees to go with him. Gaff flies Deckard to police headquarters and delivers Deckard to his old boss, Bryant (M. Emmet Walsh
). Bryant tells Deckard that a small group of Nexus-6 replicants has come to Earth illegally. Two of them were killed trying to scale a high-voltage security fence outside the Tyrell Corporation. Four have survived; Bryant shows Deckard their files. The leader is Roy Batty (Rutger Hauer
), the most advanced and intelligent of the group. The others are Zhora (Joanna Cassidy
), Pris (Daryl Hannah
), and Leon, the replicant who shot Holden. Deckard is charged with tracking them down. Bryant also tells Deckard that the Nexus-6s are believed to be advanced enough that they may have developed emotions, which might make them harder to detect via VK testing. Subsequently, the scientists designed the Nexus-6s to have only a four-year lifespan. Bryant sends Deckard to Tyrell Corp.'s headquarters to test the VK machine on a Nexus-6.
Deckard and Gaff fly to Tyrell headquarters. While Deckard awaits Tyrell, he meets Rachael (Sean Young
), a beautiful woman who welcomes him and who acts as Tyrell's personal assistant. Dr. Eldon Tyrell (Joe Turkel
) appears and questions Deckard about the Voight-Kampff test, doubting its ability to distinguish replicants from humans. Tyrell offers Rachael as a test subject, saying he wants to see a negative test result on a human before providing a replicant to be tested. Deckard asks Rachael over 100 test questions before the VK machine finally alerts Deckard that Rachael is a replicant. Rachael leaves and Tyrell explains that Rachael is a Nexus-6 and one of the most advanced replicants ever designed. She has been designed to possess memories; however, the memories given Rachael have been culled from Tyrell's nieces or other family members. Deckard is surprised to realize that Rachael doesn't know she's a replicant.
Deckard's first lead takes him to Leon's apartment. He finds a stack of photographs there, as well as a scale from an animal's hide. Not far away, Roy Batty is waiting on the street for Leon to return from his apartment. Leon appears and tells Roy that there were policemen there and he was unable to retrieve his photographs. Roy is perturbed but takes Leon with him to a shop called Eye World, owned by a Chinese man named Hannibal Chew (James Hong
), who engineers eyes for replicants for Tyrell. He is confronted in his subzero lab by Roy and Leon, the latter of whom rips open Chew's thermal coat to make it easier for Roy to interrogate him. Roy asks Chew about "inception dates," the date marking a replicant's first activation and beginning of their four year lifespan. Chew, quickly freezing to death, desperately tells them that they need to talk to Tyrell about increasing their lifespans. Roy suggests that meeting with Tyrell will be difficult, but Chew tells him that a Tyrell employee, J.F. Sebastian, may be able to gain Roy access.
Deckard takes Leon's stack of photos home with him. He is surprised by Rachael in the elevator. Deckard, seemingly feeling betrayed, is quite rude to Rachael, who was unable to talk to Tyrell himself after she found out she is a replicant. Though Rachael shows Deckard a picture of herself with her mother, Deckard insensitively quashes Rachael's insistence that she has actual memories, telling her they'd been taken from other people. Rachael leaves, extremely hurt. Later, while drinking, Deckard examines old photographs on his piano and dreams of a white unicorn. When he awakes, he examines one of Leon's photos and finds that Zhora is visible in a back room. Deckard notes that she has a prominent tattoo on her neck of a looped serpent.
In another part of Los Angeles, near an old, neglected hotel called the Bradbury, a woman walks into an alley and covers herself with waste paper to keep warm. She dozes for a bit until a man approaches her and startles her awake. She runs away, breaking the window of his van, but the man kindly returns one of her bags and she becomes friendly. The woman is revealed to be Pris, one of the Nexus-6s Deckard is pursuing. The man is J.F. Sebastian (William Sanderson
), a genetic designer for the Tyrell Corporation and the person Chew told Roy to find. Pris agrees to stay at Sebastian's place, where he designs lifelike toys and dolls.
Deckard visits the crowded streets near Chinatown and has a old Asian woman examine the animal scale. Deckard believes it to be from a fish but it's from a snake and, like most animals of the time period, is artificial. A serial number is also visible under the microscan; it identifies the maker as a man named Abdul Ben Hassan (Ben Astar
), whose shop is right up the street. Deckard confronts Hassan, who tells him he'd made a snake for a dancer working at a club owned by Taffey Lewis (Hy Pyke
). Deckard goes to the club and places a quick call to Rachael, apologizing for his insensitivity and asking her if she'd like to join him at the club. Rachel refuses.
Deckard finds that Zhora is an exotic dancer at the club and she uses artificial snakes in her performances. Deckard poses as an irritating private eye investigating abuses by club owners who may spy on female performers. Zhora sees through Deckard's ruse, beats him violently, and dashes from the club into the streets. Deckard quickly catches up and chases her until he's able to shoot her. Zhora crashes through several plate glass windows and falls to the street, dead. When a passerby examines Zhora, they see the snake tattoo under her ear.
Bryant arrives on the scene and talks to Deckard, congratulating him for finding and retiring Zhora. He tells Deckard that there are four more replicants to retire; Deckard insists that there are only three left. Bryant tells him that Rachael has disappeared and Deckard now has to find her. Deckard spots her a few moments later across the street. As he follows her, he's suddenly grabbed by Leon, who beats him severely. As Leon appears poised to kill Deckard by stabbing his fingers through Deckard's eyes, his forehead explodes; he has been shot by Rachael using Deckard's own pistol, which Leon had batted from Deckard's hand a few moments before. Deckard returns to his apartment and Rachael joins him. Deckard appears to be much more sympathetic toward Rachael since she saved him from Leon. When she asks him if he'd hunt and retire her, he tells her he wouldn't, but someone else surely would. He gives her a drink and the two play together on Deckard's piano. Deckard becomes more amorous and Rachael rejects his advances. Deckard prevents her from leaving his apartment and the two have sex off screen.
Pris wakes up in Sebastian's apartment. She talks to him about his strange skin condition, "Methuselah syndrome," which makes him age quickly -- he is only 25, but looks older. Suddenly, Roy appears (likely summoned there by Pris). He sadly shares the news that Zhora and Leon are both retired. Roy and Pris reveal to Sebastian that they are both Nexus-6s and they need to get help for Pris or she'll die. Pris proves to Sebastian that she's artificial by grabbing an egg from boiling water and tossing it to Sebastian, who finds it too hot to handle. Roy notices that Sebastian plays chess and asks him about his opponent, who is Tyrell himself. Roy convinces Sebastian to use his connection to Tyrell to arrange a personal meeting. Sebastian reluctantly agrees.
Roy and Sebastian go to Tyrell's pyramidal home and take an elevator to his penthouse. They are stopped as a security measure but are allowed to proceed when Sebastian voices two moves to Tyrell himself that win the chess match they'd been playing; the last move is given to him by Roy. In Tyrell's bedchamber, Roy confronts his creator, saying specifically he wants an extension of his short lifespan and calls Tyrell "father." (In the 1982 Theatrical and 1992 Director's editions, Roy says "fucker" in place of father.) Tyrell explains, with technical details, that artificial beings like Roy have been permanently designed not to live longer than their lifespan and that no known biological process has yet been able to change that. Roy becomes more despondent, telling Tyrell he's done "questionable things." Tyrell patronizes him, saying he's also accomplished great things. Roy, still despondent, first kisses Tyrell, then begins to crush his skull, poking his thumbs through his creator's eyes. Tyrell falls dead and a horrified Sebastian, unable to escape, is killed off screen by Roy.
Deckard flies in his car to the sector where J.F. Sebastian lives. He receives a report from Bryant, who tells him that Tyrell is dead and Sebastian has been found dead at the same scene. Deckard places a call to Sebastian's apartment claiming to be a friend. Pris answers the call but hangs up without a word. Deckard has to move his car when some street people climb on the back, apparently hoping to scavenge parts they can sell. Deckard enters Sebastian's apartment and searches for evidence or leads. The apartment is full of lifelike toys and mannequins. As Deckard searches the mess, he is surprised by a disguised Pris, who assaults him using acrobatics. As she performs a series of back flips to finish Deckard off, he shoots her through the abdomen. She twitches violently for a few moments before Deckard shoots her twice more and finally kills her.
Roy finds Pris dead and kisses her lifeless lips. Deckard shoots at him, and Roy chides him that he's "not being very sporting to shoot an unarmed man." Roy stalks Deckard, seizing Deckard's hand through a wall and deliberately dislocating and breaking two of his fingers in memory of Zhora and Pris. Deckard escapes to an upper floor in the building but is easily found by Roy, as he howls from the pain of trying to reset one of his fingers. Deckard keeps moving, but is in great pain and drops his gun. Roy is already showing signs of his own impending death -- he stabs himself through the hand with a large nail to temporarily stabilize his condition. Deckard seizes an opportunity to beat Roy with a large pipe but he cannot incapacitate Roy, whose superhuman strength is too much for Deckard. Deckard eventually escapes to a window ledge. Deckard climbs to the roof, but Roy appears moments later. Deckard tries to jump to another roof across the street. He nearly plummets, hanging on by one hand. Roy makes the jump quite easily and peers over the ledge at Deckard, saying "Quite an experience to live in fear, isn't it? That's what it is to be a slave." Deckard slips and Roy catches his arm with one hand, dragging him to safety. Roy sits down near him, holding a dove he found on the other roof, and tells Deckard that he's seen more in his short life than most humans would see in a full lifetime. Roy is saddened by the idea that all the memories he's acquired will be lost "like tears in rain." Then, echoing the last thing Leon said to Deckard, Roy says "time to die" -- but he's referring to himself. As he finally dies, the dove in his hand flies off. In the original theatrical version (1982), the rain has stopped and the dove flies toward a clear blue sky. In the Final Cut (2007), the rain continues and the dove flies toward an overcast sky. Deckard notes that the replicants only want the same things that humans do.
Gaff meets Deckard on the roof and throws his pistol back to him. He congratulates Deckard on completing his investigation; Deckard tells him he's officially finished with hunting replicants. As Gaff walks away, he looks back over his shoulder, and yells, "It's too bad she won't live, but then again, who does?", referring to Rachael.
Deckard returns to his apartment and is alarmed to find the door ajar. He takes out his gun and calls Rachael. When she doesn't answer he walks through the rooms with his gun drawn. In the bedroom, Rachael is completely covered by the sheet. He fears that she is dead. Much to his relief, she wakes up when he pulls the sheet back and touches her. He asks her whether she loves and trusts him; she replies that she does. A few minutes later, she is dressed and Deckard, after checking the lobby outside his apartment, motions for her to join him in the elevator. On the floor of the lobby is a small origami unicorn, left there by Gaff. Gaff's words about Rachael not living echo in Deckard's head. He realizes that Gaff was there but let Rachael live. Deckard studies the unicorn for a moment, then crushes it in his hand. In the Final Cut and Director's (1992) editions, the film ends when the elevator doors close. In the Theatrical edition, Deckard and Rachael drive into a mountainous area and Deckard explains in voice-over that Tyrell told him that Rachael has no termination date. Echoing Gaff's sentiment atop the roof, he muses, "I didn't know how long we had together... who does?"