The mysterious Julius Borden (James Callis), arrives in Camelot with news of a magical secret that threatens to change the landscape of the kingdom forever. But just how far is Merlin prepared to go to put things right? Would he really risk everything and reveal his secret?

As the dust settles, Camelot is left devastated.

For amongst the assembling guests lurks a deadly assassin (Phil Davis) set to strike.

But Arthur's old adversary, Odin, promises to ensure this is one party Camelot will never forget. The mighty citadel is buzzing in anticipation of the Prince's birthday celebrations. Friendship and loyalty are tested to the limit, but in the end, it's the power of love that changes all their lives forever… Though the Knights know their journey to the Isle of the Blessed is fraught with danger, none could anticipate the sacrifice Arthur intends to make there. As Lancelot (Santiago Cabrera) races back to Camelot with the dying Merlin, Arthur must continue on his mission to vanquish the Dorocha without them. The second episode of this two parter finds the kingdom on the brink of collapse and Morgana poised to strike. But it will take more than just swords to vanquish their enemy and Merlin is shocked to the core when he discovers the only way to restore the equilibrium requires a sacrifice of unimaginable proportions… With Uther a shadow of his former self, it falls to Arthur and his loyal Knights, including Lancelot (Santiago Cabrera) to protect the kingdom. Hellish creatures pour forth, killing any who succumb to their touch. With her magic stronger than ever, the sorceress summons the mighty Callieach (Gemma Jones) to tear open the veil between the worlds. Merlin faces his toughest challenge yet when Morgana's blinkered determination threatens not only Arthur's future, but the very balance of the world. Merlin must keep his magic secret or face being executed by Uther.Season 4 Episode Guide Episode 1 - The Darkest Hour, Pt. When Merlin meets Arthur, he believes that he is arrogant and Arthur, likewise, views Merlin as subservient. The dragon tells Merlin that he plays an important role: to protect Uther's son, Arthur, who will bring forth a great kingdom. He discovers that the king, Uther Pendragon, has outlawed magic and imprisoned the last great dragon deep under the kingdom. Merlin is a young warlock who arrives in the kingdom of Camelot after his mother arranges for him to stay with the court physician, Gaius. s04e13 - The Sword in the Stone (Part 2 of 2).s04e12 - The Sword in the Stone (Part 1 of 2).Season 4 Episode 12 of Merlin resulted in a 0.00 rating in the 18-49 demographic. It is down to Merlin to try and save Arthur from Morgana's clutches. After the sorceress strikes everyone is forced to run for their lives including Arthur. Morgana is now the head of a vast Southron army and a deadly net is closing around Camelot.

Merlin season 4 episode 12 full episode