Three police officers work surveillance on a major insider trading investigation. One night one of the officers, Yeung (Louis Koo), learns in advance that the stock price of the company under investigation is going to rise. He convinces his colleague Lam (Daniel Wu) to delete the recording so that he can take advantage of the tip. When suspicious trading the following day sees the relevant stock suspended, all three officers are caught on a spiralling path of poor choices to keep their money and avoid being arrested themselves.

The writing partners Alan Mak and Felix Chong made a hell of an impression in Hong Kong when their first screenplay, Infernal Affairs, became a commercial and critical smash hit. It was later remade by Martin Scorsese as the American thriller The Departed. The subsequent films Confession of Pain and Lady Cop and Papa Crook – which they also directed – firmly established them as two of Hong Kong’s finest creators of crime and police thrillers, a reputation they more than uphold with their 2009 feature Overheard. As a financial thriller it uses a comparative minimum of action and violence, yet as the plot thickens and the protagonists’ increasingly desperate attempts to stay afloat pile up it forms one of the very best Hong Kong thrillers I have ever seen.

There is a strong sense of constant failure to the story. Yeung, Lam and their supervisor Leung (Lau Ching-wan) make a terrible mistake in attempting insider trading. When they try to correct their mistake, they make another one – and can either admit to their original crime or allow one of the original men under suspicion to be murdered. When they take a third route and try to take justice into their own hands, they wind up being recognised by the victim’s girlfriend. On it goes, with each choice leading to a worse one, spiralling relentlessly towards a catastrophic conclusion.

In a typical move for a Hong Kong thriller Overheard is not afraid to take bold storytelling choices. There is a genuine feeling to the film that anything could happen, and that no character is safe from harm. It gives the story an edge that Hollywood equivalents often struggle to match.

The film also benefits enormously from its lead cast, with Daniel Wu, Louis Koo and particularly Lau Ching-wan developing strong and believable characters with their own specific strengths and failings. Lau in particular is remarkable. His character Leung is sleeping with his supervisor’s estranged wife, and is the most honest of his team. When their greed threatens to put them both in prison, he is reluctantly dragged into their conspiracy out of loyalty and friendship. Lau plays conflicted emotions brilliantly. His character spends the film torn between his friends and his better nature, and Lau ensures the pain of that tension is palpable.

Overheard is a slick, intelligent and regularly surprising thriller with a smart screenplay, effective direction and strong performances. Mak and Chong followed it up with two thematic sequels, each of which featured the same cast of actors in completely new surveillance and finance-based roles. It is an interesting concept for a franchise, united only by cast and subject matter, and I am very keen to see how each sequel plays out.