Leung Siu Tong (aka Laughing) was originally an upstanding citizen and was highly motivated to become a law enforcer. Tong enlisted and was accepted along with his love interest, Wendy, to become a cadet. While in between training, he was approached by captain of the "Organized Crime and Triad Bureau" (OCTB), Captain Kwok, to seriously consider doing undercover work (due to his high aptitude scores). While interested in bringing down the triads, he was also conflicted to accept such a mission and bet his future with the flip of a coin to decide his fate (a habit he'll develop to decide all major decisions). The coin decided his future to become an undercover agent. From then on, it became a decade's worth of playing the dangerous game of spying for the HK police and paid the price for his job.
To successfully enter the triads, he began a long road of lies and deception, to fool everyone that he's changed for the worst. He got himself "expelled" out of the academy and began spending time with unsavory characters. His sudden behavior change and negative actions convinced Wendy to abandon him and Tong silently missed Wendy throughout his life. Over time, his escapades allowed him to work under Yik-Tin (leader to one of the largest triads in HK) and developed his triad nickname, Laughing.
While he successfully entered Yik-Tin's organization, his trust level was low and had minimal chances for him to be close to him. He eventually succeeded in gaining Yik-Tin's attention and trust after he saved him from a rival gang's assassination attempt. While he successfully gained Yik-Tin's trust, he nearly killed himself as he was severely wounded in the process; he survived the ordeal and started climbing his way to the top while continuously reported his actions in his diary for his commanding officer.
In between the 8-10 years, his undercover identity was well sealed. Yik-Tin never suspected him and almost moved up to become his right-hand-man, but he was never given any special orders to help build evidence to take down Yik-Tin. Laughing's greatest desire is to access Yik-Tin's naracotics operations to generate further evidence to arrest him. Around this time, Yik-Tin's "beloved" triad brother was released from jail, Kong Sai-Hau. With Hau in the mix, his ability to gain attention and respect lowered, affecting his credibility as a triad gangster in the scheme of things.
Laughing knew that Yik-Tin was insecure about Hau's return. Yik-Tin previously promised to split half of all he has to Hau as long as he accepted and help him suffer a decade-long jail sentence. Upon returning, Yik-Tin had Laughing pull a series of bullying and instigation tactics to rattle him to make sure Hau wouldn't do anything to risk his command. Helping Yik-Tin in this endevour allowed him greater trust and eventually moved into the triad's narcotics division.
After Yik-Tin showed Laughing of his secret narcotics drug lab, Laughing clued in the police to have Yik-Tin arrested. This was Laughing's last action to help in the capture of Yik-Tin and have him prosecuted in jail. Yik-Tin's life would be cut short as he tried to run for his life away from the cops, only to be shot down by officer Pak-Kiu. With Yik-Tin dead, Hau was the next in line for power. After a brief power struggle, the triad elders ultimately decided on Hau to be the new triad leader of their organization. Laughing in between this time was ready to return as a true policeman, only to be asked to continue his services.
OCTB felt that Laughing can still do good if he continues to spy Hau. Laughing was conflicted again as he understands the importance of bringing down Hau, but he also wanted to return to being a regular cop. Face with this decision, he once again bet his life upon a flip of the coin, he stayed as Laughing for the triads. Around this time, officer Chung Lap-Mun entered Hau's gang as a new flunky as he was expelled from the force. Laughing theorized he was undercover, but had no evidence to prove he was otherwise. He continued to treat Mun as if he was an enemy to continue his false persona.
Sometime later, there was a biker gang that attacked civilians and Hau ordered a hit on them after one of them attacked his girlfriend's mother. Laughing and Mun teamed up to hunt them down. While separated, he saw Mun talking to officer Pak-Kiu to negotiate the apprehended biker over to the police. From then on, Laughing would quietly trail Mun to make sure he didn't get caught. Both Mun and Laughing would eventually know of each other's undercover identities and even develop a special bond with each other. Laughing eventually felt this bond would affect both their lives and decided to play a stronger villainous role to cause Mun distance himself away him.
Ultimately, Hau figured out that Laughing was undercover. However, he also suspected Mun as a traitor as well. Hau wanted to see proof of Mun's sincerity into the triads by having him kill Laughing. Laughing and Mun were traveling together under assignment, but Hau already called Mun to make the kill to prove to him that he's no cop and cleaning his hands of Laughing's death. While in a abandoned old shack in the forest, Laughing and Mun staged a realistic fight seen to allow prying eyes see a believable struggle of life and death. While Laughing continued to pretend he's trying to kill Mun, officer Pak-Kiu happened to encounter the situation and thought that Mun's life was in mortal danger and shot Laughing.
Mun quickly recovered a mortally wounded Laughing and intended to send him to the nearest hospital by van, but Laughing refused. Laughing knew that any deviation from their original plan of staging his death would've made Mun suspicious. He then told Mun to finish the job to continue his undercover work. In his final moments, Laughing told Mun he had no regrets and that heaven was kind to him. He also gave explicit instructions to Mun of where to find his diaries in his room. In the end, Laughing intentionally pulled Mun's gun and fired into his heart. His death secured Mun's triad loyalties and Laughing's bloody corpse was used to confirm Hau of Mun's loyalties.
Though Mun managed to convince Hau of his loyalties, Laughing's death would haunt him. In respect for Laughing, he went to his room to recover his diaries. Through his own hand-written words, Mun recounted Laughing's life and understood all he has done. In honor of Laughing, Mun developed his habit of flipping a coin to make serious decisions when he couldn't.
Some analysis have been made about how this phenomenon happening in Hong Kong. Because of his popularity, Hong Kong Television Broadcasting station (TVB) signed a contract with the actor for a movie that solely features Laughing. The movie is entitled Turning Point (Chinese: Laughing Gor之变節).
This is the first time in history where a fictional character's death from a TV drama has been mourned in reality in Hong Kong.