In 1948, the People's Liberation Army launched the Liaoshen Campaign, and some cities were liberated first. Chencheng was one of them. However, the multiple shadows of the Kuomintang's hidden spies, stragglers, habitual thieves and bandits made Chencheng fall into a dilemma of chaos without fighting, and chaos and depression filled every corner of this big city. In order to enable the masses to regain vitality and meet challenges under the new regime, Qin Tianliang, a former underground party member, took over as the director of the Chencheng Military Control Commission. Qin Tianliang led the director of the Investigation Department Ji Liancai, the director of the Security Department Sun Dahu, and the investigation consultant Yelu Qi who returned from studying abroad to carry out a transformation work. Yelu Qi has always been skeptical about the new regime. Although he is a private detective expert, he has always kept a distance from the cadres at all levels of the Military Control Commission with the attitude of doing things one day at a time. But inspired by these new Communist colleagues and influenced by their role models, he finally turned into a staunch fighter. He used his reasoning skills to unravel the case layer by layer, and with the help of his leadership and his colleagues, he finally smashed the conspiracy of hidden spies to assassinate the central leaders.