HBO Asia's first Original series, a ten-episode detective noir series set against the tumultuous backdrop of 1960s Singapore, when the global balance of power is shifting and Singapore is at its crossroad; a time when the British colonial rule is coming to an end, independence is on the horizon, and the island state can finally forge its own identity.
When the Cheng Detective Agency is hired by the CIA to investigate the murder of a US sailor, Sam is asked to help out as a favour to the widowed owner, Patricia. But as Sam tries to save the life of an innocent man, he is forced to revisit memories of killing a childhood friend during the second World war.
Forced to flee to China during the Japanese occupation, Feng returns to Singapore looking for her husband whom she has not seen since the war. No one is certain that he was still alive, yet Sam and Patricia, both of whom know what it is like to lose loved ones agree to help solve this mystery of Feng's husband. The case then gets more convoluted when Feng is mysteriously poisoned.
While delivering some photographs to a client, Patricia gets hurt when caught up in a major riot sweeping through the streets of Singapore. She is taken to safety by a photo journalist named Hafiz. After realizing that her photographs were stolen, it dawns on her that this was a deliberate attack. Soon after, Hafiz is accused of being involved with the riots, and Patricia and Sam work to prove his innocence. The trail leads them to a secret MI6/Special Branch operation against subversives.
While trying to sort out Kang's gambling debts, Sam is reluctantly drawn into the detective agency's investigation of whether Claire Simpson's husband, Frank, has been accepting kickbacks from clients. If the allegation is proven to be true, Frank's boss, Maxwell Black, will kick Frank out of the company and Singapore, separating and Sam and Claire forever.
When Claire discovers that the medicine by Maxwell Black's company to children at a small village hospital is not working, she insists that the company investigate the problem. Sam somehow manages to prove that the genuine drugs are being diluted. He also goes on to find out that families will eventually turn to expensive black market substitutes when they realize the ineffectiveness of the hospital medicine. Further investigations help Sam to recognize that this is all part of an elaborate scam run by the Secret Society.
When a newborn baby is left on the doorstep of the Cheng Detective Agency, Patricia and Sam try to figure out what they are to do with him. Patricia also receives a package containing Winston's fob watch, which was believed to be stolen when he was murdered. Meanwhile, Su Ling confronts her fear and desire over her relationship with Conrad, and Kang strikes a deal with the Devil.
Caught transporting explosives, Kang will face the gallows if Sam is unable to track down the truth about Lim Chee Kit, a leading trade unionist whose organization is suspected of being involved in a recent bombing. The case is further convoluted because Chee Kit's brother, James, is a well-connected businessman with political aspirations. Although he disagrees with Chee Kit's politics, James hires Sam and the agency to find and help his estranged brother before the police arrest him.
When Sam goes out on a limb for an ex-World War II Australian soldier who had been accused of murder, no one understands why he is so adamant on the man’s innocence - least of all Macca, who had been in love with the girl who was murdered. Either gaol the accused man for life or Sam has just made a very big mistake about his hero and friend.
Sam is on the brink of discovering the truth behind the murder of Patricia's husband - a murder that involves a secret deal between James Lim, Kay Song and the CIA. But is he obsessed with solving this case in order to avoid facing the fact that he might lose Claire forever?