The Quest book by Wilbur Smith

Egypt has been struck by a series of terrible plagues, killing its crops and crippling its people. Then the ultimate disaster befalls the kingdom: The Nile fails. In desperation, the Pharaoh sends the warlock Taita, wise in the lore of the gods and a master of magic and the supernatural. But not even he could have imagined what terrible enemy waits in ambush in those dark lands at the end of their world. Now it's up to Taita to save Egypt--before the end of the world's most glorious civilization draws near. Published By St. Martin's Paperbacks on 2008-02-05