Bodies are turning up in the dark city streets - some horribly mutilated, others with an equation w¥Äz = Cov (w,z) = ©¬wzVz carved into their flesh. As Detective Argo (Skarsgard) and his new partner (George) unearth the meaning of the equation, they realise that each victim is being offered a gruesome choice - kill your loved ones or be killed.