High in the mountains, a great horde gathers; Morgana prepares for war with a vengeful Mordred at her side. Merlin feels the weight of his destiny like never before as the ancient prophecies play out ...

At 50, Merlin—the greatest magician in the kingdom— would like nothing more than to retire to the woods and live in peace. But with the arrival of the fairy Viviane and young Lancelot, Merlin's plans ...