Lucy (Scarlett Johansson), a student studying in Taiwan, find herself an unwilling drug mule for crime boss Mr. Jang (Choi Min-sik). When she accidentally ingests the synthetic CPH4 which has been surgically implanted in her abdomen, she rapidly develops advance physical and mental abilities as the drug unlocks the unused parts of her brain. However, this process also puts her life in peril and she soon realises that she requires further doses of the CPH4 to stay alive. Striving to reconcile herself to her situation Lucy reaches out to Professor Samuel Norman (Morgan Freeman), a neuroscientist and expert in the hidden capabilities of the mind. Meanwhile, Mr.Jang does not take kindly to interference in his drug trafficking and sets out to hunt down Lucy.