An arrow from a renegade knight. Aimed at Arthur. He is too far away to place himself in its path, so he stops it midflight. Arthur turns just in time to see his eyes change from gold to blue.
At dawn the wagon pulls up to a block with dried red stains running down either side. The headsman leans on his axe casually. They force him to kneel and rest his head on the block. Uther is proclaiming his crime to the crowd, but he doesn't listen. Merlin hears the axe fall and sits up in bed, shaking. A nightmare.