New servant, Cedric (Mackenzie Crook), muscles in on Merlin's position as Arthur's right-hand-man and turns the prince against his loyal friend. Merlin is convinced the slippery newcomer is up to something and he's right -- Cedric is a conman and a thief who's after a magnificent jewel recently unearthed in a tomb far beneath Camelot. Little does Cedric know, his precious prize is more dangerous than he could possibly imagine. Camelot has never been more vulnerable but how can Merlin make things right when, thanks to Cedric, he might have lost Arthur's friendship for good? Merlin faces the prospect of turning to the creature he swore he'd never trust again - The Great Dragon.