Every contact leaves a trace Every clue serves as a silent witness against crime Bomb disposal expert Yeung Yat Sing (Kevin Cheng Ka Wing) returns from England to visit relatives and he comes across a grenade case by accident. With his tactful and level-headed approach, Sing is highly appraised by Senior Chemist Ko Yin Pok (Bobby Au-Yeung Chun Wah) and is being invited to join the Forensic Division. In a little while, Sing becomes the division's rising star. By work, Sing gets back in touch with his long-lost best friend Koo Chak Sam (Frankie Lam Man Lung). Sam serves as a forensic writer and he is going to get married soon. Accidentally, Sum's fiancée Lam Ding Ding (Linda Chung Ka Yan) is killed in an explosion and Pok's police girlfriend Leung Siu Yau (Yoyo Mung Ka Wai) also loses the ability of holding a gun in the incident. Yau's duties are passed to Ma Kwok Ying (Charmaine Sheh Sze Man) from the Narcotics Bureau. Both Sam and Sing 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…