Echoes in the Dead of Dawn (слэш)

The spell rolls across the field, flattening the grass with all the howling power of a gale-force wind. As the wave of magic crashes against them, Merlin has no time to gasp out a spell. He only throws up his arms to cover his face, his own sorcery flaring around him in the same defensive instinct — twin reflexes, beyond conscious thought.
OR: On a morning patrol outside the castle, the knights encounter a sorcerer hell-bent on revenge. Merlin can save Arthur, but doesn't realize what it will cost him until it's too late.