An Lan, once famous in the martial arts and underground world, chose to retire to obscurity. Twenty years later, at the entrance of the law enforcement bureau, she is reunited with her twin sister An Mei, whom she has been separated from for twenty years. At this time, An Mei's fate is tragic; her husband He Wenyuan has been framed by villains, incurring heavy gambling debts, and she herself is seriously ill. Before her death, An Mei entrusts her daughter Tian Tian and the shattered He family entirely to her elder sister. An Lan decides to take on her sister An Mei's identity, infiltrate the He family, seek justice for her sister, and protect Tian Tian.