里昂（让·雷诺饰）是名孤独的职业杀手，受人雇佣。一天，邻居家小姑娘马蒂尔达（纳塔丽·波特曼饰)敲开他的房门，要求在他那里暂避杀身之祸。原来邻居家的主人是警方缉毒组的眼线，只因贪污了一小包毒品而遭恶警（加里·奥德曼饰）杀害全家的惩罚。马蒂尔达得到里昂的留救，幸免于难，并留在里昂那里。里昂教小女孩使枪，她教里昂法文，两人关系日趋亲密，相处融洽。 
　　女孩想着去报仇，反倒被抓，里昂及时赶到，将女孩救回。混杂着哀怨情仇的正邪之战渐次升级，更大的冲突在所难免……

李昂: (Nothing's the same after you've killed someone. Your life is changed forever.) You have to sleep with one eye open for the rest of your life.
玛蒂尔达：I don't give a shit about sleeping. leon. I want love....or death. That's it.
李昂：I want death. Only death is real. Get off my case. Mathilda. I'm tired of your games.
玛蒂尔达：There's this really great game. Leon. Makes people nicer. Start them thinking. The kind of game you love. If I win you keep me with you... for life
李昂：And if you lose?
玛蒂尔达：Go shopping alone, like before.
李昂：You're gonna lose. Mathilda. There's a round in the chamber. I heard it.
玛蒂尔达：So what? What's it to you if I end up with a bullet in the head?
李昂：Nothing.
玛蒂尔达：I hope you're not lying. Leon. I really hope that deep down inside there's no love in you. Because if there is just a little bit of love in there for me...I think that in a few minutes you'll regret you never said anything. I love you. Leon.
玛蒂尔达：I win.

（只要你杀了人，你的人生就变了，什么都不同了。）你的余生都要提心吊胆的过日子。
我不管将来如何，李昂。我只需要爱....或者死。就是这样。
我选择死亡，只有死是真的。别烦我了，玛蒂尔达，我已厌倦了你的游戏
这游戏很有趣，李昂。它让人变得和善，让人开始思考。这是你喜欢的方式。如果我赢了，你一生都要陪着我。
如果你输了呢？
你还是独来独往，一如从前。
你输定，玛蒂尔达。你上满了子弹，我听见了。
那又怎样？若我中枪身亡，你会怎样？
若无其事。
我希望你没说谎，李昂。我也希望你的内心深处，从来没有爱过我。因为如果你有那么一点点爱我的话，那几分钟后，你会后悔一直没有说出自己的真实感受。我爱你，李昂。
(玛蒂尔达开枪，李昂抢下。)
我赢了。