While working on a stolen car case, a female cop and her half-brother are transported twenty years back in time where they assist their model police officer father on a gang war case. As the investigation deepens, they discover that the killer they seek might be one of their own.

Eager to make her mark and break the stereotypes surrounding women cops, officer Yang Yu-ting sets out to crack a stolen vehicle case with trainee Chou Ming-hsien in tow. Unbeknownst to others at the department, the two are actually half-siblings – their deceased father was also a police officer, the renowned recipient of a national Exemplar Medal for meritorious service. While investigating the stolen vehicle case, the siblings are accidentally transported back in time to assist their father on a gang war case that involved over thirty killings. When they return to the present, they discover their stolen vehicle now hides an important clue to solving the twenty-year-old case. It turns out the police are not only implicated in the three-way gang conflict – the murderer was actually an undercover cop!

As the lines between good and evil blur, an internal power struggle at the police department raises the stakes, forcing everyone to choose ideological sides, and calling into question the trust at the foundation of the police force. None of these developments can be separated from the siblings' paternal legacy; once seen as a deadbeat dad who cast off his wife and children, their father turns out to be a man of principle who had his reasons for keeping his distance. As the truth gradually comes into focus, all of their assumptions will be challenged, from what it means to serve as a police officer to their personal definitions of justice.

Author Yen Yu makes use of his own experiences as a police officer to lend realism to a police novel that challenges the conventional divisions between good guys and bad guys. The sci-fi element of time travel is seamlessly woven into the plot, establishing a link between cases separated by two decades while also highlighting thematic questions relating to loyalty, justice, and personal gain.