Chan Wing-Yan was an undercover sent by Wong in 1991 to infiltrate the Ngai triad. He was discovered to be the brother of Ngai Wing Hau while as a police cadet, whom Wong thought was the ideal choice to infiltrate among their ranks. He was subsequently expelled by the school as a guise. His real identity was only known by a few. Yan had a close call in 1995, when his brother purged the Big Four and everyone involved in his father's murder. He managed to remain calm and silent to prevent blowing his cover in front of his brother. However, his identity was discovered during Hau's dying moments.
Shortly after 1997, he was reassigned to spy on Sam, under his henchman Keung. He stumbled on Yeung and a Mainland triad boss Shen in early 2002. He suspects Yeung as another mole sent by Sam. During a firearms exchange with Shen's men, the three reveal their real identities through a chance meeting in the aftermath of a gun battle.
Yan was a central character during Wong's attempt to apprehend Sam during a cocaine exchange in 2002. Again his cover was almost blown, when Sam was tipped off by Lau that the mole was meeting Wong. He failed to appear when ordered to but managed to elude capture by Sam and gain his trust by pinning the mole as his long time friend Keung, who succumbed to injuries sustained during a brief skirmish between both sides. Yan then works with Lau and the OCTB team to arrest Sam succesfully.
While he waits for Lau to access the database containing his bio, he finds out that Lau was Sam's mole and abrubtly leaves the building. This proved to be his costly mistake, as Lau deletes upon finding out.
He frequently reports to Wong and Docter Lee. Yan divulges information on the triads using Morse Code as a method of communication.
Chan Wing-Yan was shot and killed by officer Billy when he attempts to enter the lift, holding Lau hostage. Shortly after his death, Doctor Yee found records of his time with the Cadet School proving his role as an undercover and Yan was posthumously recognized and given a police funeral.