Every contact leaves a trace
Every clue serves as a silent witness against crime
Bomb disposal expert Yeung Yat-Sing, Ivan, (Kevin Cheng) returns from England to visit relatives and he comes across a grenade case by accident. Ivan's skills are highly appreciated by Senior Chemist Ko Yin-Pok (Bobby Au-Yeung) and he is invited to join the Forensic Division. Ivan soon becomes the division's rising star. Sing gets back in touch with his long-lost best friend Koo Chak-Sam (Frankie Lam). Sam serves as a forensic writer and he is going to get married soon.
During a case, Sam's fiancée Lam Ding-Ding (Linda Chung) and Pok's police girlfriend Leung Siu-Yau (Yoyo Mung) are caught in an explosion meant to kill two drug dealers. Ding-Ding dies of her injuries, while Siu-Yau loses movement in her right hand. Yau's duties are passed to Ma Kwok-Ying (Charmaine Sheh) from the Narcotics Bureau. Both Sam and Ivan find Ying extremely charming with her smart and unfathomable characteristics in case handling.
Integrating laboratory techniques, logical reasoning, and forensic knowledge, the trio strive to fight against crimes tremendously. As they get to know each other more and more, the entangled triangle of love also starts to hinder their working relationships...
At the end of the series, Ivan and Ma Kwok-Ying end up in a car crash while chasing a fugitive, but through that experience, Ivan knows that Ma Kwok-Ying is committed to him, with her efforts to pull him out of the car in which they were trapped in. In the end, Ivan suffers from an explosion by a bomb planted by a fugitive to get revenge on Bell, which leads him into a coma. Right before the explosion, Ivan planned to propose to Bell. After the last case, Tim and Siu Yau get married. During the wedding, Ivan wakes up, although the frame only shows Ma Kwok-Ying receiving a call on her mobile phone, then running ecstatically, while crying, from the wedding, ripping her dress as she did in the first episode to aid running. The remaining wedding crowd finds out, and runs after Bell to see Ivan.