For three years, a serial killer has walked among the citizens of Hangzhou, China. With each new body come the same clues: a jump rope, a cigarette, and a slip of paper that says, “Come and get me.”

In the same city, Luo Wen wanders into a park just as a young woman stabs a local thug to death in a desperate act of self-defense. A former criminal investigator who lost his own family in an unsolved case, Luo Wen is familiar with the slippery nature of justice. So he makes the split-second decision to help the terrified woman cover up her crime, leaving behind no trace of evidence.

Luo Wen’s friend Yan Liang, a criminologist and professor known for solving each case like a mathematical equation, is called in to help the police on the recent homicides. As he digs deeper, he discovers more questions than answers—and variables that simply don’t add up.

While Yan Liang follows his suspicion and Luo Wen covers his tracks, a battle of wits plays out—with the winner’s version of justice as the ultimate prize.