Lucy is a 25-year-old American student living in Taipei, caught in a whirlwind romance with the charming but reckless Richard. One morning, after a night of partying, Richard convinces her to deliver a mysterious briefcase to a hotel, claiming it's just paperwork. Reluctantly, Lucy agrees, but the delivery goes horribly wrong. Richard is shot dead by unseen assailants, and Lucy is captured by a gang of Chinese mobsters led by the ruthless Mr. Wang. The briefcase contains four packets of a blue, crystalline powder—a synthetic drug called CPH4, a prototype for a new recreational substance. Wang forces Lucy to become a drug mule: the packets are surgically implanted in her stomach, and she is scheduled to fly to Los Angeles, where the drugs will be removed. Before she can leave, a guard beats her, rupturing one of the packets. The CPH4 leaks into her bloodstream, triggering a catastrophic transformation.

As the drug courses through her body, Lucy's brain capacity begins to unlock, starting at 1% and rapidly climbing. She gains extraordinary abilities: enhanced strength, speed, perception, and the power to control her own body and eventually matter itself. She escapes from the warehouse, killing several guards with chilling efficiency, and makes her way to a hospital to have the remaining pouch removed. During the surgery, she calls her mother, experiencing vivid memories from infancy and a profound sense of connection to the universe. The surgeon informs her that CPH4 is a molecule naturally produced by pregnant women to fuel fetal bone growth, but in such quantities it should be lethal. Lucy, however, is not dying—she is evolving.

Determined to understand her condition and share her knowledge before it consumes her humanity, Lucy tracks down Mr. Wang at his hotel suite. Using her newfound telepathic abilities, she extracts the locations and flight details of the other three mules. She then contacts Professor Samuel Norman, a leading neuroscientist in Paris whose theories on brain capacity she has absorbed. Norman is initially skeptical but becomes convinced when Lucy demonstrates her powers by controlling electronic devices and reading his thoughts. She arranges to meet him in Paris, but on the flight her body begins to disintegrate as her cells become independent entities. She barely manages to pull herself together, landing in Paris with the help of Captain Pierre Del Rio, a French police officer who becomes her ally.

Del Rio helps Lucy intercept the other mules at various European airports, recovering the remaining CPH4. Meanwhile, Wang's men attempt to retrieve the drugs, leading to a violent confrontation at a Paris hospital. Lucy effortlessly disables the attackers, demonstrating her growing control over matter. She then goes to the university, where Norman has assembled a team of top scientists. Lucy explains her philosophy: that fear limits human potential, that time is the only true unit of measure, and that knowledge must be shared to advance humanity. She decides to use the remaining CPH4 to push her brain to 100% capacity, uploading all her accumulated knowledge into a digital format for future generations.

In a stunning climax, Lucy's body dissolves into the fabric of the universe. Her clothes fall empty to the floor, and the scientists are left in awe. A moment later, Norman receives a text message from Lucy: "It's on Youtube." She has transcended physical form, becoming one with time and space, leaving behind a gift of infinite knowledge for humanity to decipher.

• The scene juxtaposes microscopic cell division with a prehistoric couple arguing by a fire; the man desires sex, the woman refuses, as Neanderthals watch. A feminine voiceover questions humanity's use of life, leading to the film title 'LUCY'.
• At dawn in Taipei, exhausted Lucy is manipulated and handcuffed to a mysterious case by smooth-talking Richard, who uses money and coercion to force her into a shady delivery at the Imperial Hotel.
• Lucy, paranoid and following Richard's orders, enters a hotel lobby to meet Mr. Wang. She is denied seating and watched by Richard outside. Four goons emerge; Richard is shot dead through the window. Lucy drops her case and panics, but the goons surround her, led by Tao who presses a gun into her back. Despite her cries, she is dragged into the elevator as sirens approach, mirroring a gazelle killed by lions. The scene ends with the doors closing on Lucy, captured and hopeless.
• Lucy, terrified and pleading, is escorted by four goons in an elevator. She loses control of her bladder, and Tao mocks her in Chinese. The group walks down a long hallway to the RoyalSuite, where the scene ends.
• Lucy is dragged into a luxurious hotel suite where three corpses lie in a corner. After vomiting in terror, she is interrogated by Mr. Wang, a silent Chinese gang boss with bloody hands. Despite her pleas of innocence, she is forced to open a mysterious case containing blue powder. The drug is tested on a Dutch addict, who convulses wildly before being executed. Wang then offers Lucy a job; before she can respond, a goon punches her, leaving her fate uncertain.
• Professor Norman delivers a lecture in Paris, explaining that animals use only 3-5% of brain capacity and humans 10%, while dolphins use 20%. He argues humanity's inventions stem from natural selection and poses a philosophical question about whether people prioritize 'having' over 'being.' The scene includes montages of animals and human creations, a humorous moment about a student's dolphin tattoo, and ends with a contemplative challenge to the audience.
• Lucy wakes in a sterile recovery room, disoriented and in severe pain, and discovers her lower abdomen is bandaged. After taking painkillers, two guards enter, throw a bag of clothes at her, and silently motion for her to get dressed, heightening her anxiety and dread.
• Lucy, dressed casually, is escorted into a lavish library where Mr. Wang and two white men await. She demands to know why her stomach was cut. The Limey explains they made a small slit and inserted a packet of C.P.H.4, a prototype recreational drug, which will be removed in Los Angeles. Lucy realizes she has been turned into a drug mule and, feeling faint, is restrained and led away by a guard.
• Lucy is marched to the far end of the living room where four other mules stand. The Limey gives a polite yet threatening speech, warning of prison and family reprisals. Lucy accuses him of causing thousands of deaths, but The Limey dismisses her with a cynical philosophy about pleasure. Guards hood each mule; Lucy is hooded last, and the scene fades to blackout.
• Professor Norman delivers a lecture on cells choosing between immortality (self-sufficiency) and reproduction, using contrasting montages of disasters and peaceful habitats with animal mating. The scene cuts to a blackout, then reveals Lucy under a hood in a vehicle, anxiously whispering self-reassurances to stay calm and wait to take a flight.
• Lucy is unmasked in a padded room and assaulted by three Chinese men. She resists by punching one, but is brutally beaten and left handcuffed and in pain.
• An endoscopic journey through Lucy's bloodstream reveals the CPH4 drug as a luminous milky way, igniting her veins and engulfing her heart. Externally, she contorts violently, slithers like a wounded animal, and charges headfirst into a wall before a blackout. Professor Norman's off-screen voice introduces the concept of accessing 20% of the brain's capacity, accompanied by a giant '20%' on screen.
• Professor Norman lectures on unlocking greater brain capacity, from 20% (control over bodily functions) to 70-80% (control over matter). He defends his hypothesis with historical examples despite a student’s demand for scientific proof. The scene ends with a blackout when asked about 100% capacity, leaving an ominous tone.
• Lucy, now possessing animal-like senses and cold composure, lures a guard into a sexual assault and swiftly kills him using her chains. In under ten seconds, she fashions a rope and grappling hook from debris, retrieves a gun, blows off her handcuffs, and escapes the cell.
• Lucy silently enters a room where four guards play Mahjong, kills three instantly, then is shot in the shoulder but calmly finishes the fourth. She tenders her wound, chugs liquor, eats leftovers, and extracts the bullet. She then arms herself with heavy weapons from a cabinet, loads them into a bag, and walks through a warehouse past workmen who watch but do not intervene.
• Lucy emerges from a warehouse and confronts two Asian bodyguards in a dark courtyard. She kills the first man after he claims not to speak English, then forces the terrified second man to drive her to the hospital.
• Lucy, with heightened senses, rides through neon-lit Taipei, then calmly hands a terrified cab driver two live grenades before walking into a hospital.
• Lucy confidently walks through a hospital at night, unnoticed. As she moves down a hallway, signs and conversations are automatically translated into English for her. She observes a surgical team through a round window and calmly enters the operating room, suggesting an impending change.
• Lucy commandeers an operating room, kills a patient, and forces a surgeon to remove a bag of drugs from her abdomen. During the surgery, she calls her mother, experiencing heightened awareness and recalling memories. The surgeon extracts a split pouch of C.P.H.4., a powerful brain-development drug. Lucy concludes with 'We never truly die.'
• Lucy exits the hospital at night, perceiving a tree's inner life. She gets into a car with a mute driver clutching two grenades, instructs him to stow them between his legs, then unsheathes a large knife from her bag, ready for danger.
• Lucy arrives at the Imperial Hotel, instructs her driver in Chinese to wait, and strides inside. In the lobby, she heads for the elevators unnoticed. Three bulky US tourists flirt with her awkwardly as they all enter the elevator, which closes on the group.
• On a hotel's 25th floor at night, Lucy forces a chatty tourist hostage to her target suite. She neutralizes two guards by threatening them with a silencer, then leaves the hostage to guard them with a gun. Lucy takes another weapon and enters the suite alone.
• Lucy calmly enters a hotel suite where Mr. Wang is being manicured. She sends the manicurists away, then stabs knives through Wang's hands, pinning him to the chair. After a philosophical monologue about pain and learning, she uses her psychic abilities to read his memories and extract information about the locations of other drug mules.
• The Driver, shaking and sweating, successfully deactivates a grenade outside a Taipei hotel. Lucy arrives, tosses him the keys, and encourages him to drive, but he remains panicked as they speed away.
• Professor Norman returns to his hotel suite, removes his shoes, and orders lasagna and a glass of white wine from the concierge, Nicole. He tells her to take her time, settling in for a relaxed evening.
• Lucy returns to her Taipei apartment and alarms her roommate Caroline with her newly acquired ability to perceive biological details. She warns Caroline about Franco's HIV and Caroline's own health issues, prints a Chinese prescription, and insists Caroline go to the pharmacy. Caroline, shaken and angry, eventually complies, leaving Lucy to find a photo of Professor Samuel Norman on the laptop.
• Professor Norman, eating lasagna in his hotel room, receives a call from Lucy, who has hacked his TV and phone. She reveals she has absorbed a substance granting 28% brain capacity, giving her control over electromagnetic waves, but she has only 48 hours to live due to rapid cell reproduction. He urges her to pass on her knowledge before losing humanity; she tearfully agrees and says she will arrive in 12 hours, leaving him stunned.
• At Taipei airport, Lucy, now with superhuman abilities, calls Paris police captain Del Rio to report a major drug ring. She demonstrates her powers by describing his office and causing his computer to display details of four drug mules, leaving him stunned.
• A coordinated international drug bust unfolds at four airports—Paris, Berlin, Amsterdam, and Rome—as mules are arrested and Chinese observers watch helplessly. In Rome, a mule attempts to flee but is tackled by plain-clothes officers as Marco, the narcotics chief, directs the operation via cellphone.
• Del Rio takes a call from Captain Marco Lurhesi, who confirms the four suspects have been captured. After hanging up, Del Rio grins and triumphantly tells his man they got all four.
• On a plane landing in Paris, Lucy ignores flight attendants while absorbing vast knowledge from two laptops. After announcing she learned 25 centuries in 11 hours, her body horrifically disintegrates—teeth fall out, skin peels, fingers dissolve—and she explodes into thousands of particles in the restroom.
• At Paris Airport, Del Rio identifies Lucy by her passport photo, discovers she was carrying 700 grams of drugs, and confirms a fresh scar on her stomach. Satisfied she is the target, he learns from a doctor that she is sedated and will remain unconscious for some time.
• Lucy wakes up in an airport medical facility, handcuffed and surrounded by armed officers. She calmly asks to speak alone with Del Rio, then raises one hand, causing all other cops to collapse. She demands Del Rio destroy the drug packets, but he says it's out of his hands. Lucy asserts her control by replying, 'I do.'
• Outside a Paris hospital, Tsui watches as mules are led inside. In a police car, Lucy agonizes over her growing intelligence, seeing telephone signals as green beams and a red Chinese beam. She intercepts a Chinese call, realizes they will be late, and forcibly takes over the wheel from Del Rio, who reluctantly yields.
• In a hospital waiting room, four handcuffed mules sit under guard by two cops. After one cop leaves, Chinese assailants silently disarm and kill the sentry, then execute the two remaining cops. A group of Chinese men with attache cases enter and shut the door, leaving the hallway silent.
• Lucy, a first-time driver, speeds through Paris in a police car, ignoring traffic laws while Del Rio panics. Despite his plea to slow down for the environment, she accelerates and slaloms between cars, blending tension with dark comedy.
• In a hospital waiting room, a German mule pleads for general anesthesia before surgery, but Tsui silences him with a shot to the head. The remaining mules are terrified, with one sobbing.
• Lucy and Del Rio arrive at a hospital where a drug extraction is underway. When a cop is killed, Lucy uses her powers to disarm and defeat the Chinese gangsters, then disables the doctor and extracts the final C.P.H.4 packet from a wounded mule. Amid the carnage, she tenderly kisses Del Rio, telling him he keeps her humanity alive, before they leave.
• Lucy arrives at a university in Paris and demonstrates her expanding abilities to a group of scientists led by Professor Norman. She accesses a scientist's memory of his daughter's death, elongates her fingers, levitates and morphs a sculpture, and explains that fear limits human potential, time is the only true measure, and all human systems are primitive. She states her intent to pass on the knowledge. The scene ends with Del Rio sensing he is about to lose her, and a huge '90%' fills the screen.
• Lucy, hooked to four drips of C.P.H.4, takes a massive dose to reach full potential. As the substance flows, she undergoes a profound transformation: her body merges with computers, the lab expands, and she gains control of time, rewinding Earth's history to its origins. The universe shrinks to a single cell before she disappears, leaving only her clothes. A text from her reveals the knowledge is on YouTube, leaving the scientists in awe.