"Detective Investigation Files" revolves around the professional and meticulous investigations carried out by a group of dedicated police officers. As they delve into mysterious deaths with unclear causes, they tirelessly work towards maintaining peace and security for the people. However, their demanding job often comes at the expense of personal happiness.

Cheung Dai Yong, a brilliant and astute police officer, has a track record of solving crucial cases. His trusted colleague, Lee Chung Yee, stands by his side, and together they tackle challenging and complex cases. Amidst their work, Dai Yong encounters Ko Jit, a tenacious journalist. Despite their initial conflicts, a deepening connection blossoms between them. However, Ko Jit already has a romantic partner.