Philadelphia detective John Hobbes (Denzel Washington) watches as Edgar Reese, the serial killer he helped bring to justice, is executed. However, Reese behaves oddly prior to his death, and soon after his execution killings in his style start once more. Hobbes starts receiving late night phone calls from the copycat killer, and follows a trail of clues to another detective, Milano, who killed himself in a remote cabin thirty years ago. Carved on the wall is the name 'Azazel' - translated as 'demon of the wilderness'. Hobbes realises that Reese and Milano were both hosts for a killer demon, which now has its sights set on him.