During the Republic of China period, a bizarre murder occurred in the country's largest arsenal. The deceased was killed by a "ghost bullet" - no bullet was found at the crime scene. For a while, doubts were everywhere and people were in panic. This case can be called the first strange case in the Republic of China. The case was handed over to Song Donglu (played by Liu Qingyun), a political police officer in charge of managing archives in the police station. Song Donglu, who served as a civilian, neither knew how to fight nor how to shoot, but he was meticulous and had a unique way to solve difficult and complicated cases. The passionate detective Guo Zhui (played by Nicholas Tse), who was determined to eliminate harm for the people, could not tolerate the corruption atmosphere in the police station, and joined forces with Song Donglu to investigate this bizarre murder case. How to shoot without bullets? How to make bullets disappear when they penetrate the flesh? Song Donglu and Guo Zhui did all kinds of research on guns and bullets, including firing salt bullets and ice bullets into pigs, but there was no satisfactory result. As the investigation of the case deepened, the two detectives unraveled the terrifying and gloomy murder chamber and the bizarre bullet-making device, the weirdness of which made the experienced Song Donglu dumbfounded. Just as the truth of the "ghost bullet murder" was revealed, Song Donglu and Guo Zhui were chased one after another. Policeman Xiaowu (played by Jing Boran) died tragically while shooting to cover Song Donglu and Guo Zhui's escape. The deadline for closing the case is imminent, and the fortune-teller Xiao Yunque (played by Yang Mi) inadvertently revealed the shocking secret of the "ghost bullet"...