According to The Nice and Accurate Prophecies of Agnes Nutter, Witch - the world's only totally reliable guide to the future - the world will end on a Saturday.

Next Saturday, in fact. Just after tea...The armies of Good and Evil are amassing, the Four Bikers of the apocalypse are revving up, and everything appears to be going according to Divine Plan. Except that a somewhat fussy angel and a fast-living demon are not particularly looking forward to the coming rapture - having thoroughly enjoyed life on earth amongst the mortals.

If Crowley and Aziraphale are going to stop it from happening, they've got to find and kill the Antichrist. There's just one glitch: someone seems to have misplaced him...