Overheard( traditional Chinese :竊聽風雲; simplified Chinese :窃听风云; pinyin :Qie Ting Feng Yun; Cantonese Yale :Sit Teng Fung Wan) is a 2009 Hong Kong crime thriller film written and directed by Alan Mak and Felix Chong , and produced by Henry Fong and Derek Yee . The film stars Lau Ching-Wan , Louis Koo and Daniel Wu as a trio of police officers conducting surveillance on a public company . The film was released theatrically in Hong Kong on 30 July 2009.

A major stock exchange in the world, Hong Kong attracts not only money but any who try to manipulate the market. At the Hong Kong Police Force Commercial Crime Bureau, an operation is underway to infiltrate a trading company, Feng Hua International where a man, nicknamed “Boss” is the chief suspect.

The team of Criminal Intelligence Bureau (CIB) officers , led by Inspector Leung (Lau Ching Wan) together with Yeung (Louis Koo) and Lam (Daniel Wu), installs interception devices to monitor the company’s communications. Yeung is a family man, has a wife, a daughter, and a son who is suffering from a serious illness and needs constant attention, while Lam, a young new comer to the team, is to be married to the daughter of a wealthy man. Leung is a calm experienced officer who is having an affair with Mandy (Zhang Jingchu) who happens to be the wife of his friend Lee (Alex Fong).

One night, while monitoring a conversation between the company's manager and his secratary, Yeung and Lam overhear that the stock price will surge on market opening the next day. Seeing an opportunity, Yeung asks Lam to delete the portion of the recording so he can take advantage of it. The next day, Lam opened an account at a stock brokerage house but was discovered by Leung. However, Lam has already invested in the stock on a deep loan. The stock rose quickly, but before the trio manages to sell it, trading was suspended due to unusual trading activity.

Back in the operation center, the three of them overhear a plot of murder to the manager using a listening device planted unofficially. To report the intelligence would lead them to suspicion, and ruin their future, and Lam begs Leung not to report it. Having thought about it, Leung decides instead to stop the murder themselves. They ambush the murderer as he force-feeds the unconscious manager with pills to fake a death scene.

Leung's face, however, was briefly seen by the manager's girlfriend, and this allows the "Boss" to track them down, seeking retribution, and organize the deaths of the Leung, Lam, Yeung, and his family. Because of Leung's compassion for his subordinates mistakes, and unwillingness to turn them in and seek help from the rest of the police force, he was unable to stop their unnecessary deaths.