It's 1425 AD, and for the Prehistoric Southwest, it's the end of the world. Barbaric tribes are invading from the north and the south, tribal uprisings in the west and a fanatic religious movement sweeping in from the east. All have conspired to bring the Fourth World to the brink of collapse. There's only one man on earth who knows when it will happen, and the deadly extent of destruction it will bring. Lionel Braithewaite, a 20th century archaeologist, is mysteriously propelled back in time, to a small town on the Mogollon frontier, just before the troubles begin. He alone can see the approaching doom. But what, if anything, can he do about it? And if he can't stop the Fourth World from tearing itself to shreds, is there any part of it he CAN save?