Highs and Lows (2012)

Gordon Heung and Wai Sai-Lok have been long-time collaborators in the police force, frequently working with each other to solve drug trafficking cases in the city. During an operation, Sai-Lok discovers clues that point to Gordon being a corrupt cop in a collusion conspiracy with drug dealers. Suspicious about Gordon's true intentions, Sai-Lok launches a secret investigation on him.