Set in 1960s Hong Kong, the serial tells an intriguing story on the kindbut gullible Ko Dai Hei (Wayne Lai), a stowaway who escapes to Hong Kong. There, he meets his father’s friend Kam Lo Yik (Joe Junior), a toppolice executive, who recruits him into the Hong Kong Police force.
Hei takes a bullet in the head in an accident. Although he recovers quickly from his injury, the wound dramatically alters his personality. The fragments of the bullets have activated Hei’s brain cells, turning him into a genius. Cracking numerous mystery cases almost single-handedly, Hei soon makes himself known as the British colony’s legendary detective. Despite the glory, Hei’s newfound brain turns him into someone churlishly cold, heartless, and ruthless. However, Hei retains a bit of his older compassionate personality whenever he is around his best friend and crime fighting partner, Pao Ping On (Ngo Ka Nin).
Meanwhile, Hei’s superior, Yik, begins to feel intimidated by Hei’s growing power in the police force. He sends his adopted daughter, Inspector of Police Kam Yi Wah (Sire Ma), to spy on Hei.
After meeting the courtesan Szeto Nam (Natalie Tong), who highly resembles his former lover Mui Mui, Hei takes another deeper step into darkness. Wanting to pull Hei back out to the light, On tries to devise ways to revive Hei’s older personality. The plan nearly backfires as On injures Hei in the process. Hei’s personality goes through another big change once again.