The Book of Revelation is a written work within DEXTER. Created by author John the Revelator, the Book of Revelation tells of the End of Days (a concept for the End of the World, birthing the New World) brought on upon by Two Witnesses. Travis Marshall takes it to heart that he is one of these witnesses and that Professor James Gellar is the other. Travis's goal is to bring about the End of Days by enacting each of seven signs (referred to as Tableaus).
An Early A.D. Cult known as the Enesserrette believed that this book was a Code for triggering the End of Days and later, a man named Professor James Gellar deciphered this code as seven sacrifices. Gellar would write down the notes required for each of these sacrifices, something that Travis Marshall would later discover and enact on his own behalf.
Passages from the book have been referenced multiple times in the Doomsday Killer Investigation, specifically by Mike Anderson who researches and prepares large printouts of different verses within the text.