Following the ending of the TV series "Undercover", Liang Xiaotang Laughing (played by Michael Tse) was convicted of murdering Su Xingbo (played by Bosco Wong) and sentenced to life imprisonment; Liang Xiaotang met university professor Huo Tianren (played by Francis Ng) in prison. The professor looked gentle and peaceful, but he was able to subdue the vicious "Juchuan" (played by Lam Suet) with psychological traps. In fact, the professor is a criminal psychologist with high IQ. He is good at cold reading and can see through the psychological activities and secrets of others, and control others silently. The mysterious woman (played by Janice Man) visited Liang Xiaotang in prison. She was affiliated with the Security Bureau, which is higher than the police force. It turned out that Liang Xiaotang was imprisoned to play an undercover role again. On that day, someone else killed Su Xingbo. The Deputy Director of the Security Bureau (played by Mak Cheung-ching) suspected that the whole thing was related to the black police gang hidden in the police force, so he took advantage of the situation to put Liang Xiaotang in prison for investigation. Liang Xiaotong followed closely and took the initiative to contact the target person in prison. When the former head of the Narcotics Investigation Division, "Da Qie" (played by Chapman To), was about to make progress, he found that the professor also used psychological therapy to make "Da Qie" mentally disordered many times, until he gave "Da Qie" a hint of death. A life-and-death duel between foes and friends, justice and evil, started fiercely under the situation of extremely uneven strength.