Léon (Jean Reno) earns his money as a hitman for the Italo-Mafia on the streets of New York. He lives a secluded life and, apart from his boss Tony (Danny Aiello), only maintains a friendly relationship with his potted plant. When the family of his neighbour's daughter Mathilda (Natalie Portman) is brutally killed by DEA cops, she flees to Léon. In order to take revenge on her little brother's murderers, Mathilda lets Léon train her as a professional killer.