Late night at the Gael village in Erin Island, an army of imperial soldiers under the command of the Priest Drwc invade the village only to find it empty except for the Gael Priestess Riannon. Despite her explanation that all of the villagers went hunting, Drwc threatens to have her torture until he realizes that she is the descendant of the Elf King Pwyll as he plans to use her as a living sacrifice to revive the Demon Lord Arawn so he may use his powers to rule the world. Riannon refuse to let that happen and tries to kill herself but is force to surrender when Drwc men captured two Gael children. He plans to have them killed unless she cooperates. She put under his mind control spell after she reveals her true name to him. Meanwhile, the Gael villagers return from their hunting trip lead by the tribe's First Warrior, Arthur, Riannon's older brother. When he learns on what happen to his sister from the children, Arthur leads a small taskforce to rescue his sister at the Demon Lord's Tomb. By the time Arthur arrives in the tomb's inner sanctum after fighting off the Imperial soldiers guarding the tomb, Drwc and his mages have finally revived Arawn who takes the form of an Albino man and approaches Riannon.
Arthur tries attack Drwc but can't since he has his sister under his control. Unknown to both of them, Arawn has dived into Riannon's subconscious and releases her from Drwc's spell. Drwc orders Arawn to kill Arthur but he kills Drwc instead. Despite rescuing his sister, Arthur doesn't trust Arwan since he's the Demon Lord and fights him. To prevent both of them from killing each other, Riannon wraps her red scarf around Arwan and by her tribe's traditions, she has chosen Arwan as her husband and Chief of the Gael Tribe. Arthur is shocked by her sister's decision but has no choice to accept it since as the First Warrior, he is honor bound to serve the Chief of the tribe. As Skeleton Warriors start to emerge, the three of them try to escape until they meet an old man named Ogam, who both Arthur and Arwan know, who leads them to exit with the rest of the taskforce. Knowing there will be repercussion if the Empire knew about Drwc's fate, Arthur rallies his people for the upcoming war against the Empire. Somewhere in the Empire, General Gaius of the Imperial Army has learn on what the Gaels did to Drwc and must now crush the Gael's rebellion.
As the the Gael's prepared to leave for Albion, Arawn is attacked by a girl with a bow and dagger named Morgan, which he easily subdues her. It turns out Arthur had assigned Morgan to prepared the ship to Albion but it was captured by Imperial soldiers, in order to save her honor, she tried to kill Arawn so would died honorably in battle. While both Arthur and Morgan wants to be punish for their failure, Arawn has no interest but Arthur is worried about setting a bad example for the others, Arawn proposes that, since Morgan lost a duel to him, he’ll take custody of her, effectively making her his "second wife". As Arawn leads the tribe to take over the ship and escape, he is confronted by Gaius himself who wants to confirmed that Arwan is the Demon lord himself. After revealing his reason for fighting the Empire, Arawn tries to escape into the ship but Gaius throws a dagger at him which he easily blocks. However, the dagger that hit him was made of electrum, the same material that killed Arawn a thousand years ago. As Ogam heals his wound, he reveals that the Empire came to be after a bloody civil war that ended the Albion kingdom when no heir was chosen after the King Pwyll died. Later that night Arthur has a duel with Arwan which Arwan beats him. Arthur admits that he's not fighting in the duel as the First warrior but as Riannon's brother as he wanted to know that his sister made the right choice of choosing him as her husband which Arwan promises him he will treat her well. As sunset arrives the ship has finally reach Albion.
Arawn leads the Gaels to Avalon, a city run by elves and their former capital. As Arwan open's the city's gates, they are greeted by two Houses Elves,Limwris and Ermin. While both of them know who Ogam and Arawn is, Limwris is surprised to learn that Arthur and Riannon are King Pwyll's descendants. As they give a tour around Avalon Castle, she reveals that the numbers of elves living here have dwindle and the castle was made by an angel. But the mention of an angel angers Arthur as he saw his father killed by one when he was younger. While exploring a weapons store, Arawn and Arthur are trapped by a magic spell by Epona, a merchant elf who at first mistaken them for thieves. As the Gaels hunt Giant Crabs for food using a crab flute, Arawn leaves the feast to find Riannon praying at a cliff. There he learns she is praying for the god Myrddin, who gave fire to humans and was punish by the other gods. Arawn comments the god isn't suffering anymore as he’s always with them as part of this world, which makes Riannon wonder if Arawn have meet Myrddin before in his time. Unbeknownst to them, Gaius is heading to Albion with an Armada.
Gaius decides to head to Londinium. At night, Arawn and Ogam discuss the possibility of the Empire catching on to them and how they do not have a proper defense or weaponry yet. In Avalon, Epona is polishing sword while Limwris and Ermin prepare dinner. Riannon decides to use Gael pots again, much to the displeasure of Ermin. Arthur drags Arawn on another hunting trip but find that they can not hunt as they are on another tribe's hunting territory. At dinner, Morgan becomes drunk and challenges Arthur for the title of First Warrior. Arawn permits the duel, and the drunken Morgan attacks Arthur. The duel is stopped when everyone hears the sound of a lyre. A minstrel named Taliesin comes out of the forest and plays a song for them. After revealing he knows they are of the Gael tribe, he leaves after telling them they are in the territory of the Brigante tribe. Gaius arrives in Londinium as Arawn and the Gaels go to Londinium for sight seeing. There, Gaius waits for their arrival. The Gaels ambush two soldiers carrying good bounf for the front lines. The gaels take the horses and goods as Gaius and his men watch. After defeating a man of Gaius', the carts are revealed to be a trap as they all contain sand. The Gaels decide to pull back. At night Arawn sees Arthur pracitcing with his sword. In the morning, the group go hunting, and after Morgan uses the crab flute, a humanoid girl rises out of the water and comes toward them.
The girl arrives on shore and reveals her name to be Llyr who is from a faerie tribe. She has come to celebrate the return of Arawn and is at his disposal from now on. Llyr helps the group hunt crabs. Arawn finds seal skin and they use it for a fire. At night, Llyr requests a leave of absence as she tells everyone that she lost her precious clothing which is important to her tribe. If she doesn't have her clothing, she can't return to her homeland. It turns out that her precious clothing was actually the seal skin that Arawn had burned. Ogam reveals that in her tribe if a man takes a womans clothing and can not return it, they become engaged. Therefore, Llyr is now "engaged" to Arawn. Llyr trvels back home with the group but proves to be bad at chores and housework. Meanwhile a group of soldiers and a knight named Octavia from the Empire find a wheel from the carts the Gael tribe took. The troop of soldiers head into the forest and are ambushed by the Gael tribe. After the death of many soldiers, Octavia takes command and orders a retreat. At the rope bridge, Octavia's superior cuts the bridge leading to several soldiers falling.
Arthur is seen training the Gael warriors, but Morgan sick of their excessive training is moping around in the kitchen with Limwris. Llyr also comes in feeling bad at how she can't milk a cow. Limwris suggests going to see the tournament in Londinium. After Morgan expresses this to Arawn, he tries to refuse on the basis the empire will be there. But both Arthur and Ogam side with Morgan he reluctantly agrees. Morgan hopes to find an item called the red branch by going to Londinium (something important to her) The group arrive in Londinium and are seen in a busy street (all the crowds coming to watch the tournament), Epona is seen selling merchandise. The group arrive at the coliseum to watch the tournament. The first round is a miner elf Rathty vs an Ogre, despite looking child like in appearance Rathty easily beats the Ogre.The mayor of Londinium who had stakes that the ogre would win decides to kick Rathty out on the basis of being a child (Rathty escapes their grasp). Arawn confronts Rathty and finds out Rathty joined the tournament for the grand prize ( Silvanus Steel) and Arthus offers for Rathty to join them. The next round is Octavia vs Bubulcus , Though Ocatvia beats him easily Bubulcus cheats by sending in a group of chariots with archers. Morgan who can't stand the site of this aids Ocatvia. After the match Morgan accidentally lets slip she's from the Gael tribe though for helping her Ocatvia says she will pretend she heard nothing. The final scene Rathty follows the group and after finding out Arawn is the demon king joins the group officially.
As everyone prepares to fortify the castle, Gaius returns to the Empire just in time to find out that Ludlum, the Senate's security force, has been ordered to take out the Gael tribe. Later back in Albion, Morgan stands watch at the beach and notices a ship approaching. Knowing the ship is filled with Rubrum soldiers, Ogam advises against taking the group lightly, but Arthur chooses to ignore his warning. As a result the Gael is forced to retreat to Avalon. Arthur falls into despair but Arawn brings him to his senses by punching him in the face. Rathty then says she has a good idea; at the Imperial Camp, Octavia discovers the Empire is collecting corpses but is knocked out by an Imperial soldier.
Lidia finds a bounded Octavia trapped in a box as she is to be sent to a mine as punishment by the Empire for insubordination against her superior and finding about the corpses. Lidia has a love/hate obsession with Octavia ever since she beaten her when they were young and she is angry she can not do anything against her. Meanwhile, the Gaels have come to the Imperial base to steal their supplies as payback. While sneaking into the base, Arwan finds two interesting boxes: one containing corpses, the other a tied up Octavia, which he tries to ignore. When the Imperial's learn of their presence, Arthur and Arwan distract the soldiers while Riannon and the rest escape with the supplies. By the time Lidia has come back to the base, it is already on fire and the theives have escaped.
As Octavia recovers from her wounds she begins to explore the castle and meet its inhabitants. Although most welcome her warmly Arthur is at first distrustful of having a soldier of the Empire so close at hand. When Octavia tells Arthur about his weak swordsmanship, Arthur doesn't take it and challenges her to a duel. However, she is eventually accepted by Arthur and decides to join the Gael Tribe.
Rubrum has discovered the location of the castle of Avalon and some of the Gael tribe believe that Octavia may be in league with them. However, when one of the children is put in danger, Octavia proves her loyalty and helps the Gael tribe repay Rubrum for their last encounter. Octavia also faces off against Lydia for the last time.
When Riannon is captured by Gaius, Arthur is desperate to save her but Arawn persuades him to wait until they have more information. As such Arawn uses meditation to locate Riannon and check on her safety. Meanwhile, the captive Riannon is making herself useful by healing and feeding the Imperial troops. She is surprised by Taliesin being at the camp, and eventually with Arawn and Taliesin's help, she manages to escape.
The Imperial forces led by Gaius have begun to move against the castle of Avalon. As such Arawn decides it is necessary to form an alliance with the neighboring Brigantes Tribe. However, when they arrive they meet Taliesin, and it emerges that the Brigantes Tribe's Chief is dead and there is no successor to take his place, because of a prophecy claiming that the next Chief will "...offend the Heavens...be cast into the Darkness...and be devoured by a monster...".
The Gael Tribe is in need of funds so Arawn decides to take Arthur and the others to his tomb where an abundance of treasure is buried. However, when they arrive they are attacked first by a group of Talos and then by an ogre. Rhiannon sees a vision of King Pwyll and an adult Primula before Arawn's tomb. Arthur makes a connection between a depiction of the Creator Watos and the Twelve Angels of the Heavens with Arawn. Meanwhile, Gaius is called before the Imperial Senate and accused of treason.
Feeling the threat of the Empire, the Gaels venture into the forest to head them off before they have a chance to make the first attack. As they ventured deeper, Arawn and Ogam realize that the area is enchanted with the power Gravitas (God's Gravity). Soon, they stop because a swamp is blocking their path. From the water rose their slain Gael comrades who were turned into "the living dead" by Creon's use of the Urn of Hell. Swords and arrows were completely useless against them, and Llyr and Rathty were growing weaker because of Gravitas' effects on elves. Ogam concludes that the living dead are similar to the enemies deployed in the great ancient battle who tortured the elves. He proposes to use his Fire of Genesis to defeat them but Arawn stops him because he deems there was no need to use such power against lowly foes. Arawn then uses a divine spell and calls upon Candidus, obliterating the enemy immediately. As a result, he has been purified and appears pure white, similar to what he "looked like in the past". Also, the spell has left Arawn weak with burns on his body. The white light Arthur sees returned the memory of his father being killed by a pure white being who called himself "Arawn". In a fit of rage that possesses him, Arthur stabs Arawn in order to fulfill a promise he made to kill the one who slayed his father. Arawn is left unconscious by his injury, and Arthur flees full of shame and guilt. The entire incident is reported to Gaius as he prepares to launch a full-scale invasion of Albion.
Arthur wanders in grief and guilt, horrified at his deed. Gaius attacks Avalon, but the Gaels are too disraught, as Arawn is in a coma, and Arthur has run off after stabbing him. Gaius thinks it will be an easy victory. However, Riannon talks to the warriors in the courtyard, assuring them of Arawn's recovery and Arthur's return. She then takes charge of their leadership and rouses their batle instincts. Lyr and Rathty marvel at this change in her timid nature. At the Gaels' camp, Ogam tells Morgan and Octavia, that all contact with Avalon was lost, and he suspects a trap, well-laid by the Empire. He proposes a wait of four days, and sets off to find Arthur. At Avalon, Lyr and Rathty hold off the seige towers scaling the walls. Gaius marvels at Riannon's resolve. At an old shrine, Arthur find Ogam and thinks that he is there to punish him, but Ogam tells him of his sorrow when the Second Moon fell from the sky and destoyed his homeland. He claims to be a dragon, but Arthur disbelieves him. He says he hates the enemy and that is his reason to fight, and he puts the question to Arthur. Ogam tells him he is too bound to his vow and has deserted his companions, hence losing the right to lead them. Arthur is confused, and Ogam tells him to go to "Gorsedd Arawn" or Arawn's throne to find the answer. Meanwhile, Morgan and Octavia set out alone for Avalon, fed up of waiting. The guardian boar demons attack the shrine as Arthur struggles with his doubt. In battle, he calls out Arawn's name, and realizes that Arawn was a true friend to him. He is then cleared of all doubts. At that point, an Electrum Golem stored in the shrine attacks them, and Ogam transforms to his real form - a blue dragon - and fights it to let Arthur escape. Arthur sets out for the Brigantes tribe forest.
On the third day the battle grows hotter. Riannon swears an oath on the scarf she gave to Arawn, to protect him with her life. Arawn has healed, but hasnt woken up. He sees first Myrndill, then Pwyll and Primula in his dreams. They all show him the valour with which his comrades are fighting to defend his city, Avalon. Both Pwyll and Primula assure him their deaths were not his fault. Gaius's seige towers keep proving innefective, as Lyr and Rathty have now got Morgan and Octavia to help them. He then launches the battering ram, after gainng control of the drawbridge. Riannon draws everybody back to the inner city walls to continue the defence. The battering ram breaks through the main door, and Gaius attacks in full force.
When all hopes are gone suddenly Arthur returned to their rescue together with Taliesin's tribe. Arthur screams for Arawn and as Gaius' is about to break the last line of defense Arawn shows up giving hope once more to his comrades and friends. All were enlightened with his return, especially Riannon. Arthur and Gauis had a duel and as he realized that what Arawn wants is not the way of the king but Little King he died in Arthur's hands. His last wishes were to spare his remaining soldier's lives. At the Empire's capital, a figure in white attacks and burns the Imperial Senate to death after revealing to them the death of the Holy Emperor.
With the Imperial Senate dead the Empire is in chaos and the Gael tribe faces a new enemy in the guise of the White Spirits, who are sending an army of Golems to destroy them. In order to defeat the approaching army Arawn decides to lure them to Mt. Claes and trigger an avalanche. However, he cannot do this alone and must first gain the assistance of the legendary Giants. En route to the Giants' home, Taliesin encounters first a baby dragon, and a memory calling itself "Lucifer" and promising to show him the Truth Behind the World.
In the past the 12 Angels gather in heaven and one questions why a new Angel has been created. One of the Angels, Merlinus, tells everyone that they have cannot completely perceive the will of God, so the other Angels leave the new Angel to him. The new Angel turns out to be none other than the Arawn of the past. Now in charge of Arawn, Merlinus asks him to refer as Myrddin or father and then gives Arawn the name Lucifer. As time passes, Myrddin tries to break Lucifer of the ways the other Angels see things, while further continuing his own plans for humanity. He ultimately frees a human girl from the other Angels mind control and ends the Ice Age by using the Song of Creation, but at the price of his own life.
Arawn becomes the 12th Angel to replace Myrddyn but he leaves Heaven after realizing that the other Angels have placed humanity under mind control again. He then frees Primula but as a result is cursed by the other Angels by being banished from the Heavens and losing his light. After seeing Arawn's past, Taliesin knows what he has to do. After parting with the baby dragon and leaving the cave, Taliesin gets his first look at the enemy. Elsewhere Arawn and the others defend the giants as they try to start an avalanche. Immediately after the avalanche starts, it is stopped by the snowstorm picking up. Realizing the Spirits are behind the snowstorm Arawn decides they will have to face the enemy at the foot of the mountain. Taliesin then uses the Song of Creation to end the blizzard and starts a new avalanche, destroying the Dark Army, but is seemingly killed.
As Arawn and Ogam head towards Palladium with the rest of the tribe and their allies, Arthur along with Riannon, Octavia and the elves attempt to retrieve Dyrnwyn who is capable of killing a god, the brother sword to Arawn's. Upon touching the sword, Arthur is shown a flash back of Arawn's meeting with Pwyll and how Dyrnwyn came into the elf king's possession. While watching the scene, Golems begin to surround them and the group, bar Arthur, attempt to hold them back. After the scene of King Pwyll and Arawn's meeting, he is shown Arawn who was nearly killed at the final battle and how both he and Pwyll used Dyrnwyn to seal the world off from the Heavens before Arawn had to be put to sleep to recover. Learning the truth of the world, Arthur manages to draw Dyrnwyn, ala sword in the stone style, whereby the entire area is encapsulated in a blinding white light. Dyrnwyn changes colour to its former glory and all of the Golems disintegrate. The group now head towards Palladium to rejoin their friends.
Having reunited at Palladium, Arthur and Arawn along with the rest of their party enter the tower and prepare for what they hope will be their final battle. However, no sooner do they enter than the group are separated. Octavia and Morgan find themselves in an arena where they must face off against an army of Golems. Llyr and Rathty stumble upon the Cauldron of Rebirth and decide to try and destroy it. Finally, Arawn, Arthur, Ogam and Riannon find themselves facing off against a resurrected Drwc.
As Arawn and Ogam make their way to the source of Gravitas, Arthur and the others continue to hold the upper hand against the enemy. Right as victory seems apparent, an increase in the amount of Gravitas quickly turns the tide of the battle. With things going downhill fast, Ogam prepares to use the Flames of Creation to stop the spell even at the cost of his life. As he does so, Etlym and Dyrnwyn resonate, renewing their strength. Ogam destroys the Obelisk's tip, stopping the flow of Gravitas. As a result, Rathty and Llyr destroy the Cauldron of Rebirth, destroying the Golems, allowing Morgan and Octavia to kill Creon, Mayor of Londinium, and a servant of the White Spirits. Drwc is killed by Arthur, and the group reunite at the Palladium's top, the Garden of the Sky. There they are shocked to see the Emperor's corpse, and Arawn is horrified to see the Angel Lector before them.
When they reach the top floor, they are surprised to see a beautiful garden. Riannon feels a cold presence despite the beauty of the garden. As they go further, they notice the Emperor's corpse sitting at the center of the garden, and then a voice greets them. They are shocked to see a figure in white before them. Ogam realizes that Lector the Astrologer from the Emperor's Court is the Lector, one of the 12 Angels, and the one who killed Arthur's father and framed Arawn for it. Arthur uses Dyrnwyn to destroy the Garden, which is revealed to be an illusion. A passageway to the Heavens opens, and Skeleton Warriors attack, but Arthur and Arawn manage to attack Lector. Arthur manages to wound Lector, making him furious and consequently summoning Merkadis. Ogam tells everyone that Merkadis is the one who killed Arawn before. Lector then becomes one with Merkadis. Arawn and the others are nearly killed when Merkadis destroys Palladium, but are saved by Taliesin and the Dragons.
Merkadis fires the Electrum Cannon and destroys a mountain. It then uses tentacles to scatter the army, but Arawn, Arthur and the others meet up. Ogam reveals that the only way to stop Merkadis is to use the Power of Words, but the only one who can do it is Riannon. Arawn and Arthur buy time for Riannon to remember the Words of Power; they succeed in cutting several tentacles but are unable to damage Merkadis' main body. Arawn is nearly killed by a shot from the Electrum Cannon, but seeing Pwyll in Arthur encourages him. Riannon remembers the Power of Words with help from Primula and uses it to cripple Merkadis and expose the Angel Lector who begs the Creator Watos for help before he is killed by Arthur. Later in Avalon, Pwyll tells Arawn that Arthur must now become Elf-King of Albion as Arthur Pendragon. Arthur becomes Elf-King of Albion. Limwris tells Ermin to continue writing their stories; Rathty comforts Llyr and forges a commemorative medal for Albion's rebirth. Taliesin and Epona continue their love/hate relationship, and Ogam reveals the Brigantes Prophesy's truth; Taliesin will be an errand boy for the Dragon he befriended for the rest of his life. Arawn leaves his sword at Myrddyn's memorial, and Rhiannon thanks the Morning Star for his guidance.