Enemy of God: A Novel of Arthur by Bernard Cornwell
The Warrior King has brought peace to Britain - but for how long?
Following a hard-fought victory, Arthur appears to have at last won the unity of the British Kingdoms. He turns his attention towards the invading Saxons, while Merlin begins a quest to uncover the sacred Treasures of Britain, believing they will bring the might of the old Gods behind Arthur for one last decisive battle. But the quest soon unravels the fragile peace, as bitter rivalries come to the fore and threaten to undo Arthur's successes, while those closest to him move to betrayal.