New servant Cedric 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 is right -Cedric is a conman and a thief who is after a magnificent jewel, recently unearthed in a tomb far beneath Camelot. Little does he 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 one creature he swore he would never trust again - The Great Dragon.

When Morgana's nightmares spill into waking hours, she becomes terrified that she has magical powers. Gaius is determined to keep her in the dark for her own good but Merlin won't stand by and watch his friend suffer. He knows exactly what she's going through and he knows she needs the truth. Is Merlin about to reveal his secret at last?

Wilfully disobeying Gaius, Merlin risks everything to help Morgana, not knowing what the far-reaching consequences might be. Lives are put in danger, loyalties are tested, and Morgana is reunited with the strange young druid boy Mordred, who the dragon predicted would one day kill Arthur.