SYFY will premier Merlin season four on Friday Jan 6 10/9 Central here in the US. Season 4 originally aired on October 1st 2011 in the UK and is already on DVD over there . At least volume 1 which was released November 28 2011. Volume 2 will be released on January 23 2012 along with a complete box set. US release dates for the season 4 DVD are in that will be announced stage.

The first episode for season 4 is the Darkest Hour part 1 which you can see the SYFY channels sneak peak for it below along with the trailer for the channels. The 4th season will consist of 13 episodes in all which you can view the list below.

There Darkest Hour Part 1

Merlin faces his toughest challenge yet when Morgana’s blinkered determination threatens not only Arthur’s future, but the very balance of the world. With her magic stronger than ever, the sorceress summons the mighty Callieach to tear open the veil between the worlds. Hellish creatures pour forth, killing any who succumb to their touch. With Uther a shadow of his former self, it falls to Arthur and his loyal knights, including Lancelot, to protect the kingdom. 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.

Sneak Peak

Trailer

4th Season Episodes ( Source Wikipedia )

1. “The Darkest Hour (Part 1)” – Merlin faces his toughest challenge yet when Morgana’s blinkered determination threatens not only Arthur’s future, but the very balance of the world. With her magic stronger than ever, the sorceress summons the mighty Callieach to tear open the veil between the worlds. Hellish creatures pour forth, killing any who succumb to their touch. With Uther a shadow of his former self, it falls to Arthur and his loyal knights, including Lancelot, to protect the kingdom. 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.
2. The Darkest Hour (Part 2)”- The kingdom is on the brink of collapse, with Morgana poised to strike. As Lancelot races back to Camelot with the dying Merlin, Arthur must continue on his mission to vanquish the Dorocha without them. 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. Friendship and loyalty are tested to the limit, but in the end, it is the power of love that changes all their lives forever…
3. “The Wicked Day”- The mighty citadel is buzzing in anticipation of the prince’s birthday celebrations. But Arthur’s old adversary, Odin, promises to ensure this is one party Camelot will never forget. For amongst the assembling guests lurks a deadly assassin, set to strike. As the dust settles, Camelot is left devastated. But just how far is Merlin prepared to go to put things right? Would he really risk everything and reveal his secret?
4. “Aithusa” – The mysterious Julius Borden arrives in Camelot with news of a magical secret that threatens to change the landscape of the kingdom forever. He has located the final part of the key to the tomb of Ashkanar, an ancient mausoleum which holds a very special treasure: the last remaining dragon’s egg. Merlin is understandably drawn in by Borden’s news, and promises to help him. But just who is the enigmatic stranger and, more importantly, why does he really want with the egg?
5. “His Father’s Son” – For the first time since his coronation, Arthur finds out what it’s really like to be King. Arthur faces his first true test as King when he incurs the wrath of the formidable Queen Annis. With the lives of thousands hanging in the balance, Arthur must find the strength to be his own man and become the leader Camelot so desperately needs.
6. “A Servant of Two Masters” – When Merlin falls into Morgana’s hands, he becomes a deadly weapon in her fight for supremacy. Using ancient magic, she pits friend against friend and creates the perfect assassin. An oblivious Arthur is in great danger. Will anyone notice Merlin’s unusual behaviour before he does the King some serious harm?
7. “The Secret Sharer” – Morgana joins forces with enigmatic wizard named Alator to uncover a secret that could change the course of destiny. With allies on both sides of the castle walls, can anyone stop her before Merlin’s mystery’s secret is revealed?
8. “Lamia” – When the menfolk of Guinevere’s home village fall victim to a mysterious illness Gaius sends Merlin, along with Guinevere and the knights, to cure them but they are side-tracked by a waif-like girl, Lamia. Only Merlin and Guinevere suspect, rightly, that she is a witch and soon the knights fall under her spell, succumbing to the same sickness. Arthur rides out with Gaius,who has realised the girl’s secret, but will they rescue Merlin and Guinevere or can Merlin defeat Lamia without revealing his magic powers?
9. “Lancelot du Lac” – When Sir Lancelot returns from the dead, old feelings reignite. Gwen must fight temptation before she commits an unspeakable act of betrayal; one that would destroy the legacy of Camelot forever. With heads and hearts thrown into turmoil, Merlin becomes suspicious. Can a man really defy death, or is there something more sinister at play?
10. “A Herald of the New Age” – The Camelot Knights stumble across an eerie shrine deep in the forest, its chilling atmosphere betraying a dark history best left undisturbed. But when Elyan ignores Merlin’s warning, his actions spark a chain of events more frightening than anyone could possibly have imagined.
11. “The Hunter’s Heart” – Morgana finds a powerful ally in the Southron warlord Helios. Together they hatch the perfect plan to force Camelot to its knees… With the Kingdom – and Arthur – preoccupied by the arrival of the beautiful Princess Mithian, it falls to an absent friend to raise the alarm. But with past wounds still raw, can love really conquer all when Guinevere returns? Or is a deadly arrow destined to fly straight into the heart of Camelot?
12. “The Sword in the Stone (Part 1)” – With Morgana at the head of a vast Southron army, a deadly net is closing in around Camelot. When the sorceress strikes, the ferocity of her attack forces everyone to run for their lives – even Arthur. But Morgana won’t let him escape that easily. And so begins a chilling hunt. Can Merlin save the King from Morgana’s clutches? Or has Arthur’s luck finally run out?
13. “The Sword in the Stone (Part 2)” – Morgana and Helios have successfully captured Camelot, and Merlin and Arthur are outlaws on the run. Trapped in Ealdor with a ruthless army closing in, their situation becomes desperate. Arthur must take control before Camelot is lost forever… But faced with Agravaine’s betrayal and the strength of Morgana’s force, the young King has lost his conviction. Only Merlin can restore his faith, and only an extraordinary act can prove to the King that he was born to rule. Will the young warlock convince Arthur before his dreams of Albion fall to pieces?