Léon spends his time being send deals for various contract killings by his boss Tony to make ends meet financially. He often lives a quiet life and starts the day off each morning working out (via doing stretchings and quick sit-ups) and watering his garden of plants.
One day, he becomes the unlikely guardian of an orphaned girl named Mathilda, who's abusive parents have just been killed by Norman Stansfield and his corrupt gang of cops. Léon starts to feel a bit of sympathy which is the first he's done in awhile given his unrespectable reputation as a cleaner. He ends up having to help this confused child learn how to kill should the day come and help find a place for her to grow up in despite the hostile environment around her while also dodging Stansfield's various raids on his apartment.