为了调查上市公司[风华国际]涉嫌的内幕交易案，香港警方派出刑事情报科的截听小组协助。梁俊义(刘青云)督察是截听小组的主管，行动中他和同胞杨真(古天乐)及林一祥(吴彦祖)，乔装进入[风华国际]，设下偷听及监视仪器，展开窃听行动。可是一个月的监听行动，仍是一无所获，小组士气开始低落；同时，梁俊义正陷于感情三角；杨真发现自己患上不治之症；林一祥又被坐拥百亿身价的未来岳父利诱他弃警从商。

一次偶然的机会，三人从窃听仪器偷听到[风华国际]的负责人罗耀明与几名高层正计划将公司股价进行炒作。当时，杨真急需要一笔安家费做身后之用，林一祥急欲与未婚妻脱离岳父的阴影，梁俊义为了两个好友，在无奈之下而决定向上司隐瞒这一消息。然后在股票市场下注，赚下这笔应急钱。

结果，[风华国际]的股价升直停板，三人无法即时套回资金，借下的高利贷逼在眉睫，三兄弟几近决裂。一个夜晚，梁俊义偷听到[风华国际]高层内讧的消息，主席罗耀明为了私利，决定趁股价高企，而暗中沽出股票套现离场，到时股价肯定一泻如注。岂料，这为他引来了杀身之祸。

意外得知此事的三人，在良心和理智下，决定以人命为重，梁俊义想出绑架罗耀明这个两全其美之计！[风华国际]终在周一复板，股价比偷听得来的情报更可怕，疯狂的飙升，三人发了一笔千万横财后，就将罗耀明放走，以为神不知鬼不觉，但是…。

At the Hong Kong Police Force Commercial Crime Bureau, an operation is under way against insider trading involving Feng Hua International, a listed company. The interception team at the Criminal Intelligence Bureau is sent in. Led by Inspector Johnny Leung (Lau Ching wan), the team has veteran cop Gene Yeung (Louis Koo) and the young rookie Max Lam (Daniel Wu). They infiltrate Feng Hua International to install interception devices and start to monitor the company phone traffic.

A month goes by and nothing significant has been intercepted. The three are bored and morale is low when they overhear the management plan to boost the share price. As Gene and Max are desperately in need of money, Johnny unwillingly withholds this information from his supervisors. The two decide to make the most of this opportunity and buy heavily on the company shares with a huge sum of money borrowed from a loan shark. Johnny is furious when he learns this, but nothing can be done at this point to retrieve the money now locked up in the shares.

The share price of Feng Hua International has gone so high that trading is suspended. The three fail to retrieve the capital and are on the verge of turning against each other in face of the crisis. Meanwhile, Johnny catches a dispute in the company’s management. The Chairman, Ringo Low, is planning to sell high and cash out his shares.

Low’s life is at stake. However the trio is well aware that if he lives, the share price will plunge and not only their money, but their lives and even their families will be compromised. The three are torn between money, their future and justice. Finally, Johnny comes up with a perfect plan: to kidnap Low…