"Iron Detective" tells the story of Inspector Sheung Sing (played by Benjamin Yuen), who was originally a rising star in the police force. During an operation, he was shot in the brain by a gangster while trying to save his comrades. After rescue, he miraculously survived and worked harder than before to solve the case, winning the reputation of "Iron Detective". However, Sheung Sing suffered from the sequelae of the shooting, including the shadow of the gunshot wound, irritability, and even incontinence. The mysterious relationship between Chief Superintendent Wan Heihua (played by Kara Hui) and Bingo (played by Philip Keung) also made the truth of the shooting confusing. In the year of the police force's big promotion, Sheung Sing was forced to be involved in the vortex of power struggle among the top police officers...