There is something horribly wrong with the bodies found in the dark city streets. Some are mutilated while others have the Price equation (w?z = Cov (w,z) = ?wzVz) carved into their flesh. Detective Eddie Argo and his new partner Helen Westcott unearth the meaning of the odd equation and realise each victim is being offered a gruesome choice: kill your loved ones, or be killed. Before long it becomes clear that the perpetrator has suffered a similar fate and is now coping by seeking a way to solve this philosophical dilemma.