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 Merlin comes across a secret chamber, he accidentally releases a goblin. The mischievous little creature possesses Gaius, making the wise and renowned court physician turn into a shadow of his former self, quickly developing a taste for gold, ale and magical jokes. To make things worse, the king suddenly becomes bald and a nasty scourge of flatulence hits the royal household. Will Merlin be able to figure out the source of all troubles, return the gobblin back to where he came from and put an end to the havoc before any real damage is done?