S3, E3: Merlin stumbles across a secret chamber and accidentally releases a Goblin. The mischievous creature possesses Gaius, leading the once wise physician to develop a taste for gold, ale and magical jokes. With a suddenly bald King and a scourge of flatulence sweeping the royal household, can Merlin work out what is going on and banish the Goblin back to where he came from before any real damage is done?