Neil Gaiman wrote the adaptation himself and ran the show, having promised Terry Pratchett he would, which makes this an unusually direct line from book to screen. The first series follows the novel closely: Aziraphale and Crowley's arrangement, the misplaced Antichrist, Agnes Nutter's prophecies, the Four Horsemen updated, and the Them. Whole exchanges are lifted from the page. The one large addition is deliberate and acknowledged: the cold open covering six thousand years of the angel and the demon's friendship, written for the screen because the book carries that history in asides a camera cannot.