Well-worn by years of gangland brutality, veteran Detective Eddie Argo (Skarsgard) prides himself on playing by the book. However, loyalties wane as he and his new rookie partner Helen O'Mara (George) find themselves entangled in a string of violent and horrific killings. Bodies are turning up in the dark city streets - horribly mutilated and with a mathematical equation cut into the victims' corpses, but what does it mean? In the midst of mounting terror, as Detective Argo and his new partner unearth the meaning of the equation, they realize that each victim is being offered a gruesome choice - kill their loved ones or be killed.