Old Wu, once a top assassin, lived a peaceful life under an assumed name at the Renxintang Pharmacy. However, this tranquility was shattered when single mother Song Xiaoqian was kidnapped by a gang. To rescue Xiaoqian, Old Wu returned to the underworld, engaging in a life-or-death struggle against a criminal gang led by Third Master and Zuo Lun. In the process, Old Wu uncovered the truth behind the murder of his wife and daughter ten years prior, discovering that the mastermind behind it all was none other than Master Xiang, whom he once respected. Ultimately, with his superb martial arts skills and unwavering conviction, Old Wu avenged his family and the innocent by killing his enemies and delivering justice.