The story took place in the 1950s, and in the drama, Long Fei was not only skilled in martial arts, but also a master of reasoning. In order to find the "informant" who betrayed the underground party leaders and eliminate the secret agents hidden in the shadows, Long Fei and his companions launched a thrilling investigation. During the investigation, Long Fei would unravel layers of fog, uncover numerous murder cases, and ultimately identify the 'informant'.