The film opens in 1987, at the 10th birthday party of a young girl. Her grandfather offers her a locket and tells her that she should share it with the one she loves most. The film then shifts to 2007. A 30-year-old woman ,Kleio Rapti, spends a night at a nightclub, in the company of her boyfriend and her best friend. After leaving the nightclub, the boyfriend proposes marriage to her. She accepts, but the young couple fall victim to a hit-and-run accident. Kleio is killed instantly, while her boyfriend is crippled and disfigured. The drunk driver responsible for the accident is put on trial, but is found innocent. He owes his freedom to a false witness, a crooked judge, a corrupt lawyer, and a medical doctor who lied under oath. The film skips ahead to 2015. The persons involved in the case are brutally murdered one by one, and the only clues left by the killer in each crime scene are the number 220 and quotes from Pythagoras. Criminology professor Dimitris Lainis is asked by the police to help investigate the case. Since his own father is comatose following a hit-and-run accident, Lainis finds himself increasingly sympathetic to the murderer's POV.