Set in the New York Metropolis, Leon, a professional assassin played by Jean Reno, is commissioned to kill by the owner of the restaurant. When he appears as a killer, he is calm and mysterious, and the killing method makes one's blood boil. But when he takes off the killer mask, then returns to become ordinary ordinary people, simple to even basic ID card, bank account also has, every day at least drink a cup of fresh milk, like watering flowers and carefully wipe the leaves of beloved potted plants, is a dual role playing people. In the apartment where Leon lives, someone is secretly smuggling the drug trade, the police anti-drug team disguised as gang members, in order to find drugs to invade, killed the drug dealers, but the family missed the little girl Matida. Matida in order to be safe and hide next door Leon home, she accidentally discovered Leon's killer identity, in order to protect themselves and revenge, Matida asked Leon to train her to become a real professional killer in a firm tone... Meanwhile, the police are also searching for Matida and detaining him... Leon alone into the police station to kill, the police panic, ordered to encirclement and raid the building and all out for Leon, the two sides of the war triggered a tension to stimulate the ultimate kill.
故事發生在紐約大都會裡，由讓·雷諾所飾演的職業殺手萊昂，受餐廳老闆委託殺人。當他是以殺手的身份出現時，冷靜而神秘，殺人手法令人熱血沸騰。但當他卸下殺手面具時，則又回歸成為平凡的市井小民，簡單到連基本身份證、銀行帳號也都有，每天至少喝杯鮮奶，喜歡澆花及細心地擦拭心愛盆栽的樹葉，是個具有雙重身份角色扮演的人。而就在萊昂所住的公寓內，有人暗渡陳倉的進行毒品交易，警方緝毒組偽裝黑幫份子，為查緝毒品而入侵，殺了販毒者一家人卻遺漏了小女孩馬蒂達。馬蒂達為了安全起見而躲進隔壁李昂家，她無意中發現了萊昂的殺手身份，為了保護自己及報滅門之仇，馬蒂達以堅定的口氣要求李昂訓練她成為一位真正的職業殺手……在此同時，警方亦全力搜尋馬蒂達並拘禁之……萊昂隻身闖入警局大開殺戒，警方大驚慌之餘，下令圍剿大廈並全力搜捕李昂，雙方交戰之下引發了一場緊張刺激的終極追殺。
Leon is 40 years old, he is a lone professional killer, and always adhere to the principle of not killing women and children; Matilda, on the other hand, is just an ordinary 12-year-old neighborhood girl. Such two people's life trajectory is not related to each other, the original will not have any intersection, but only because the latter unfortunately killed the disaster made two people accidentally came together, and between them also produced a wonderful chemical reaction: love.
萊昂已經40歲了，他是一名習慣獨來獨往的職業殺手，並且始終恪守著不殺女人和孩子的原則；而瑪蒂達卻只是一個普通的12歲的鄰家女孩。這樣的兩個人的生活軌跡本互不相干，原來也不會有任何交集，然而只因後者不幸慘遭滅門之禍才令二人意外的走到了一起，並且在他們之間還產生了一種奇妙的化學反應：愛情。
This looks at first glance some unimaginably strange, after all, the age difference between two people is too big, but think carefully, but again in the reasonable.
這乍看起來有些匪夷所思，畢竟兩人的年紀相差太大，但細細一想，卻又在情理之中。
Although Leon has reached the middle age, and is silent and cruel, witty and able, but under his solemn appearance, there is hidden a gentle, kind, innocent and simple pure heart. For many years, the killer life of living alone makes him feel lonely and lonely, and the only bright color in life is the pot of tequila. He nursed it as if it were his life, and before he knew it, the plant was his only friend in life -- even, in his eyes, a second self. Although the girl Matida is still young, and looks so weak and helpless, but her life experience and tragic special encounter make her character become very headstrong, independent, and has a maturity that is not commensurate with her age. For her, Leon is indeed a trustworthy and reliable object, and she for Leon, is it not the latter in the dark life of the ray of golden sunshine suddenly appeared? The same is the end of the world reduced people, plus a long time of contact moisten and foam, life and death together, so the two have the same lonely and eager to warm the soul of nature more and more close, finally rub out a subtle spark.
萊昂雖然已年屆中年，而且為人沉默冷酷、機智幹練，但在他不苟言笑的外表下，卻深藏著一顆溫柔善良、天真質樸的赤子之心，多年來離群索居的殺手生活令他倍感孤獨與寂寞，生活中唯一的亮色就是那盆龍舌蘭。他把它當成自己的生命一樣來培育，不知不覺，這盆綠色植物成了他生活中唯一的朋友——在他眼中，它甚至就是另一個自己。而女孩瑪蒂達雖然年紀尚小，且看起來是那般的柔弱無依、楚楚可憐，但她的生活經歷以及悲慘的特殊遭遇令她的性格變的非常的倔強任性、獨立自主，而且還有著與年齡極不相稱的成熟。萊昂對於她而言，固然是值得信賴與依靠的對象，而她對於萊昂而言，又何嘗不是後者黑色生命中那縷突然出現的金色陽光呢？同是天涯淪落人，再加上長時間的相濡與沫，生死與共，於是這樣兩個有著同樣孤獨且渴望溫暖的靈魂自然越走越近，最終擦出微妙的火花。
Although Leon finally in order to save Matida and sacrificed his own life, but he will not regret falling in love with her. Because it is she, let him relive the joy of life, feel the sweetness of love, and completed the redemption of his own soul (he finally washed his SINS with his own blood); While Matida, I believe that she will not regret giving her first love to the middle-aged man named Leon, because it is he, so that she can get protection from harm, relive the warmth of the long lost family, and understand the true meaning of love, and learned how to cherish.
雖然萊昂最後為了救瑪蒂達而犧牲了自己的性命，但他一定不會後悔愛上她。因為是她，讓他重溫了生活的樂趣，感受到了愛情的甜美，並且完成了對自身靈魂的救贖(他最終用自己的血，洗清自己曾犯下的罪孽)；而瑪蒂達呢，相信亦不會後悔把自己的初戀給了那個叫萊昂的中年男人，因為是他，讓她得到保護不受傷害，重溫久違的家庭的溫暖，並明白了愛情的真諦，且學會了該如何去珍惜。
Never regret falling in love with you, the longer you go the more you cherish. If the light can flow back to the past, I must also be with you again music, because, you are the only one in my life.
從不後悔愛上你，走得越久越珍惜。若時光能流轉回到過去，我也一定還要與你再共譜戀曲，因為，你就是我今生的唯一。