“Something's going down in the up.”

Aziraphale and Crowley, of Heaven and Hell respectively, have grown rather fond of the Earth. So it's terrible news that it's about to end. The armies of Good and Evil are amassing. The Four Horsemen are ready to ride. Everything is going according to the Divine Plan...except that someone seems to have misplaced the Antichrist. Can our heroes find him and stop Armageddon before it's too late?