After Kwong Yiu is arrested in 2018, he joins the crime unit undercover. There's a new 1993-style murder. The suspect has escaped from the psych ward.

Kwong Yiu and Hoi Ching investigate prime suspect Mak Chi Hung and find evidence to invalidate his alibi. Kwong Yiu asks about Hoi Ching's parents.

The crime unit links the serial murder case to the 1990 King Shun Building fire. Kwong Yiu discovers his daughter lost her memory in a car accident.

Officer Yip is secretly monitoring Kwong Yiu. Kwong Yiu asks Tin Ming to help him verify if Hoi Ching is his daughter. Hoi Ching steps into danger.

Kwong Yiu rescues Hoi Ching. Mak Chi Hung warns Kwong Yiu of a mole in his team. Kwong Yiu finds the mole dead and is mistakenly arrested for murder.

Mak Chi Hung helps Kwong Yiu to escape. Hoi Ching discovers that Kwong Yiu is her father. He investigates an underground bank but is taken hostage.

Kwong Yiu and Ah Fu fight. Mak Chi Hung kidnaps Shek Tat Chi to learn the truth about the fire. Kwong Yiu follows Shek's wife to an empty locker.

Shek's wife is found dead, then Shek dies. Coroner Chan is found unconscious after he's kidnapped by Mak Chi Hung. Tin Ming has a crush on Hoi Ching.

Mak Chi Hung is arrested and admits to killing for revenge. Kwong Yiu tells Tin Ming he believes the real killer is Coroner Chan. Hoi Ching is upset.

Kwong Yiu is shot saving Mak Chi Hung from a sniper attack. He recovers and asks Mak Chi Hung to reveal his mentor. Tin Ming tracks Chong Hiu Wa.

Mak Chi Hung kills himself with a pen hidden by Coroner Chan. The crime unit discovers that Blind Biu is using Chong Hiu Wa's paintings to ship drugs.

Hoi Ching sets a trap to test Coroner Chan. Chong Hiu Wa is kidnapped by a masked man and threatened. Chan admits he was the Man in Black from 1993.

Man Yi and Tin Ming find evidence that puts Chan's identity in doubt. Tin Ming asks Chong Hiu Wa to introduce him to Sundess so he can go undercover.

Chan sets Sundess' base on fire. Tin Ming knocks out Sundess and takes his hard drive. Wai To dies protecting Tin Ming. Kwong Yiu arrests Chan.

Kwong Yiu tries to return to 1993 but fails. Sundess' evidence self-destructs. Sundess eats the police's takeout and is poisoned. Man Yi is a suspect.

Man Yi confesses she has been seeking revenge, and Pui Kit's murder was arranged by Sundess. In a gun battle, Hoi Ching takes a bullet for Man Yi.

The serial murder case is solved. Kwong Yiu returns to 1993 and reunites with his family. He gives up his police job but continues to hunt down evil.