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.
Short Description BBC One
Below is the recap of this episode, which may contain spoilers if you have not seen it yet!
One year has passed since Morgana tried to become queen of Camelot. King Uther is only a shadow of his former self who has never overcome Morgana's betrayal. Prince Arthur has taken over the leading of the kingdom with the help of his uncle Agravaine. For Merlin life at Camelot has returned to normal with his daily chores for prince Arthur. Aside of Gaius Merlin has found in Lancelot one more friend he does not need to hide his magical abilities from.
A patrol of Camelot knights encounter one day a black clad woman dragging a cart. As it turns out it is Morgana whose magical powers have grown. She defeats the knights and continues on her way to the Isle of the Blessed with her sister Morgause in the cart who is severely ill.
When word reaches Arthur that Morgana has shown up, he sends out patrols to capture her being puzzled that after a year of hiding she has now been seen. He also worries about what she might be up to. Arthur is deeply grateful for his uncle Agravaine to have helped him through the past months. That same night a feast takes place celebrating Samhain, the time of year when people are the closest to their ancestors.
Samhain is also the time of year where the gate to the veil of the dead can be opened. Filled with hatred Morgause convinces Morgana to kill her and use her blood sacrifice to open the gate so that their enemies will fall to their knees and she wants Morgana also accept it as her last gift to her. Morgana performs the ritual.
Back at Camelot Merlin is affected by the opening of the gate, hearing the cries of the dead and seeing an old woman right in the middle of the hall calling over and over again Emrys. He collapses at the feast. Lancelot and Gaius bring the unconscious and freezing Merlin into his room where Gaius claims he has never felt someone being that cold. It's a mystery to Gaius what has happened to Merlin and sends Lancelot to get blankets and hawthorn to get the blood pressure going.
The old woman also shows to Morgana and introduces herself as being the Cailleach, the gatekeeper to the spirit world accusing Morgana to have torn the veil between the two worlds. The voices come from the Dorocha which are the voices of the dead. The Cailleach warns Morgana that tearing the veil has created a new world and she foretells that the one called Emrys will walk in Morgana's shadow and that he is her destiny and he is also her doom.
When Merlin wakes up he is shocked to the core. He has felt the Cailleach' voice as coming from the depth of the earth, her eyes so sad oozing so much pain. Gaius explains to Merlin who she is. He also believes that it was no coincidence that the Cailleach has shown and that Merlin due to his powers was easily the only one having such visions. But Merlin denies it being a vision. He claims it was as if she knew him and that she had called him by his name Emrys. Gaius is not sure what it means but he becomes very concerned about the fact that someone might have opened the spirit world.
The next morning the young village girl Drea tells Arthur at the council chambers that her village had been attacked by shapes without faces. They had moved quickly and felt unreal and the people were screaming and then there was only silence. All had been killed.
Arthur takes his knights and a skittish Merlin to the village to investigate. What they find makes Merlin's skin crawl. The village seems utterly deserted except for a few animals that are left behind. When night falls they find a couple of dead people who have seemed to be shock frozen and they hear screaming voices.
Still not knowing what they are actually dealing with, they spread out to investigate the village further. Merlin can feel the spirits and when he gets separated from the others he uses his magic to bring a little light into the dark night. But his magic ceases to work when he gets attacked by one of the Dorocha. It is Lancelot who saves him with a blazing torch. Merlin realises that the spirits are not something one can chase or kill and Arthur with his knights retreat from the village.
Back at Camelot the spirits have shown as well, attacking people. It seems that the mere touch of them lets people freeze to death instantly and only fire can repel them for a while but not kill them. While Gaius covers one dead after the other with blankets a devastated Merlin confess to him that his magic is useless against the spirits. He felt a deep emptiness when the spirit came for him back at the village and he could not breathe. Merlin is deeply scared.
Gaius figures out that the shapes are the Dorocha, the spirits of the dead. On Samhain Eve at the time of the old religion, the high priestess would have performed a blood sacrifice and release them. Now it could only have been Morgana who was seen to have been travelling to the Isle of the Blessed, a place of the old religion. Gaius also tells Arthur that the Dorocha cannot be defeated and that no mortal has ever survived their touch.
While Camelot prepares for another night by putting as much fires on as possible Arthur tells Merlin that he might be more scared as Merlin is. More and more people from across the kingdom seek refuge at Camelot and Arthur is desperate for a solution to vanquish the Dorocha. Gaius tells him that if he is right the Dorocha can only be defeated by repairing the tear in the veil on the Isle of the Blessed. In order to do so and since a blood sacrifice was necessary to open the gate Gaius assumes another blood sacrifice must be made to close it.
Arthur is prepared to do lay down his own life, something Merlin cannot allow to happen.
At a hut in the forest Agravaine meets Morgana to bring her the news that Arthur is about to head to the Isle of the Blessed in order to sacrifice his own life and thus to vanquish the Dorocha. Morgana is troubled about the news and the prophecy the Cailleach had made about the one they call Emrys she has never met and does not know who he is. Agravaine tries to dispel her fears telling her that within a week Arthur would be dead and the throne be free for the rightful heir.
Back at Camelot Arthur says goodbye to his father who does not want Arthur to leave him, feeling that Arthur is about to do something drastic. Also Gwen feels that something is not right and also asks Arthur to stay. She asks Lancelot to look out for Arthur and to bring him home. Meanwhile Arthur gives the royal seal to Agravaine in order for him to deal with the kingdom's business while he is absent and to take the throne in case something happens to his father.
Merlin is also packing intending to accompany Arthur and his knights to the Isle of the Blessed. Despite his magic being useless against the Dorocha he still feels it is his destiny to protect Arthur. And if it is his destiny to sacrifice himself in place of Arthur so be it. Gaius is not able to talk him out of that and thus Merlin, Arthur and the knights of Camelot leave on their journey to the Isle of the Blessed.
Shortly before night Merlin volunteers to collect wood and Lancelot follows him trying desperately talking Merlin into leaving since he has no powers and he does not want him hurt. "You are not a warrior, Merlin. I do not want to see you hurt." "It is your duty to protect Camelot no matter what the cost. Well, it is my duty to protect Arthur."
Back at the hut Morgana has a nightmare in which she sees herself lying on a battle field begging an old Emrys to help her. "Is this really what you wanted, Morgana?" Waking up she now has seen Emrys for the first time and she has the urge to kill him.
By nightfall Merlin, Arthur and the knights reach Daelbeth and gather as much wood as possible but are interrupted by Dorochas attacking them. Soon they realise that the collected wood is not enough to get them through the night and Arthur volunteers to collect more with Merlin ready to help him, dismissing the others by letting them know that he is actually the servant knowing how to collect wood after all. Lancelot has a nagging feeling of foreboding.
When Merlin gets attacked Arthur saves his life and both flee into one of the old castle's rooms. It becomes freezing cold in the room but it seems only Arthur can feel it. He also wonders about him not ever having worried of dying before and Merlin tells him he should not start to worry about that now. Merlin also believes and Arthur agrees if things had been different the two would have been good friends.
When one of the Dorocha makes it through the door and Arthur wanting to protect Merlin, Merlin pushes him aside jumping right in the Dorocha's path and getting flung across the room. At the same time Lancelot who felt the two of them gone too long and the knights break through the door with torches repelling the other Dorocha.
Running towards where Merlin lies both Arthur and Lancelot can see that Merlin is covered in ice flakes with his eyes open and being unresponsive.