Lucy is a 25-year-old American woman living and studying in Taipei, Taiwan.
She is tricked into working as a drug mule by her new boyfriend, whose employer is a Korean mob boss and drug lord named Mr. Jang.
Lucy delivers a briefcase to Mr. Jang containing a highly valuable synthetic drug called CPH4. After seeing her boyfriend shot and killed,
she is captured and a bag of the drug is forcibly sewn into her abdomen and that of three other drug mules
who will also transport the drug for sales in Europe. While Lucy is in captivity, one of her captors kicks her in the stomach, breaking the bag,
releasing a large quantity of the drug into her system. As a result, she begins acquiring increasingly powerful
and enhanced physical and mental capabilities, telepathy, telekinesis, mental time travel,
and she can choose not to feel pain or other discomforts, in addition to other abilities.
She kills off her present captors and escapes.
Lucy travels to the nearby Tri-Service General Hospital to get the bag of drugs removed from her abdomen.
The bag is successfully removed, and Lucy is told by the operating doctor of the volatile nature of the drug and its destructive side-effects.
Sensing her growing physical and mental abilities, Lucy returns to Mr. Jang's hotel, kills his bodyguards, assaults Mr. Jang,
and telepathically extracts the locations of all three drug mules from his brain.
At her shared apartment, Lucy begins researching her condition and contacts a well-known scientist and doctor, Professor Samuel Norman,
whose research may be the key to saving her. After Lucy speaks with the professor and provides proof of her developed abilities,
she flies to Paris and contacts a local police captain, Pierre Del Rio, to help her find the remaining three packets of the drug.
During the plane ride she starts to disintegrate as her cells destabilize from consuming a sip of champagne,
which made her body inhospitable for cellular reproduction. Only by consuming more CPH4 was she able to prevent her total disintegration.
Her powers continue to grow, leaving her able to telepathically incapacitate armed police and members from the Korean drug gang.
Lucy recovers the drug and hurries to meet Professor Norman, with whom she agrees to share everything she now knows,
after he points out that the main point of life is to pass on knowledge. Jang and the mob also want the drug and a gunfight ensues with the French police.
In the professor's lab, Lucy discusses the nature of time and life and how people's humanity distorts their perceptions.
At her urging, she is intravenously injected with the contents of all three remaining bags of CPH4.
Her body begins to metamorphose into a black substance, spreading over computers and other objects in the lab,
as she transforms these into an unconventionally shaped, next generation supercomputer that will contain all of her enhanced knowledge of the universe.
She then begins a spacetime journey into the past, eventually reaching the oldest discovered ancestor of mankind, implied to be Lucy,
and touches fingertips with her. Meanwhile, back in the lab, after an M136 AT4 destroys the door,
Mr. Jang enters and points a gun at Lucy's head from behind, intending to kill her. He shoots,
but in an instant before the bullet strikes, Lucy reaches 100% of her cerebral capacity and disappears within the space time continuum,
where she explains that everything is connected and existence is only proven through time.
Only her clothes and the oddly shaped black supercomputer are left behind. Del Rio enters and fatally shoots Mr. Jang.
Professor Norman takes a black, monolithic flash drive offered by the advanced supercomputer created by Lucy's body before the machine disintegrates to dust.
Del Rio asks Professor Norman where Lucy is, immediately after which, Del Rio's cell phone sounds
and he sees a text message: "I AM EVERYWHERE." With an overhead shot, Lucy's voice is heard stating,
"Life was given to us a billion years ago. Now you know what you can do with it."