Rage of a Demon King (The Serpentwar Saga, Book 3) - E. Raymond Feist

The third novel in the bestselling Serpentwar Saga. The ultimate darkness approaches . . . As the Emerald Queen's shadow lengthens once more across the land of Midkemia, her forces stand ready to launch a devastating invasion. Come the battle's dawn, the magician Pug and his life-long friend Tomas will discover that something far worse than the Queen's sorcery is afoot. For an insatiable nightmare creature has entered their world, seeking to own and corrupt the source of life itself. When the final conflict is joined, reptile will stand against man and magician against demon; and those who battle for good must be victorious . . . or all is doomed.