Chicago detective Doug ‘Sharkey’ Bremner and his partner, Pepe Aloise, are confronted with a hideously brutal murder in an alley beside a bar on January 13th. The main suspect, Maurice, met the victim earlier that day. Maurice’s identical twin brother, Roland, provides an alibi, but Sharkey cannot lose the feeling that Maurice is somehow responsible. There is no evidence - just his cop’s instinct. Two equally bizarre killings took place in the previous months on the same date. The detectives believe they are the work of a manic serial killer murdering victims every thirteenth of the month. While Pepe is not convinced, Sharkey knows in his heart the murderer is Maurice, but cannot prove it. February 13th is getting closer, and Sharkey knows there will be another killing. But with nothing connecting the three victims and no evidence to arrest Maurice, Sharkey must take matters into his own hands, which leads to a horrific discovery.