Merlin: Season 3, Episode 12

3 - 12: The Coming of Arthur: Part One

Arthur and Merlin retrieve a magic artifact on a mission, the cup of life. However, they are captured by a slave trader known as Jarl. They are rescued by Gwaine, but when they are found, the artifact falls into the hands of Morgause and Morgana. Morgause uses the cup of life to form an immortal army. Can they be stopped?