Excalibur: A Novel of Arthur
Excalibur: A Novel of Arthur  is a historical fiction novel by English writer by Bernard Cornwell, the third and final book in The Warlord Chronicles series. The trilogy tells the legend of Arthur seen through the eyes of his follower Derfel Cadarn.

Plot

Part One: The Fires of Mai Dun
The novel begins shortly after the end of Enemy of God. Arthur has taken full control of Dumnonia and Guinevere is imprisoned. Mordred, while still king, has had his power taken away from him. Lancelot has joined with the Saxons and Derfel is trying to deal with both his daughter's death and his service to Arthur. Meanwhile, the two Saxon kings, Aelle and Cerdric, have put aside their differences to work as a combined front against the British kingdoms. Although Arthur has united Dumnonia, Powys and several Irish kings to his cause against the Saxons, Gwent refuses to fight. King Meurig offers to fight against the Saxons but only if he is given Dumnonia's throne, as Arthur does not want it and Mordred is no longer considered fit to rule. However, Arthur and the other kings refuse his demand.

Merlin is preparing for a pagan ceremony at Mai Dun, that is said will bring the Old Gods back to Britain. Before the ceremony though, Derfel must go and try to make his father Aelle turn against his ally Cerdic. Upon arrival Cerdic demands Derfel's death but Aelle says his son must fight a Saxon in single combat and if he wins he will be allowed to live. Derfel wins and stays the night but is unable to get his father to stop his attack on Britain.

It is finally the time of Mai Dun the ceremony is not completed though due to Arthur realising that Nimue intends to sacrifice his son to bring the gods forth. Arthur's part in stopping the ceremony earns him the hatred of many pagans in Britain, who blame him for preventing the gods' return.

Part Two: Mynydd Baddon
Finally the Saxons invade. Derfel, along with Ceinwyn and Guinevere, leads a group of survivors who are trapped at Mount Baddon. Derfel is impressed by Guinevere's efforts in the battle, as she uses several tricks to hamper their enemies' forces, winning them much needed time and victories until Arthur reaches them. Eventually, Arthur arrives along with Sagramor and Cuneglas and manage to win a victory over the Saxons. He also succeeds in convincing Gwent to fight by appealing to Tewdric, Meurig's father who had abdicated to become a monk. Tewdric briefly reclaims his throne from his son and leads Gwent's thousand spears in battle against the Saxons.

During a respite in the fighting, Liofa, Cerdic's champion, humiliates a Powysian warrior before the British and Cuneglas tries to fight him but is killed, costing Arthur his staunchest ally and Derfel a man he considered a brother. Despite assistance from Tewdric, the Saxons still outnumber the British and, despite their heavy losses, they are likely to win the battle. However, after the British push back two assaults and expect the third to finish them off, Cuhlwch and Irish king Oengus mac Airen arrive with fresh troops and Merlin, who uses the dead body of a killed prince riding into battle to terrify the Saxons who believe a ghoul is attacking them. The Saxons are beaten and Cerdic flees with his army in ruins while Aelle's remaining forces are surrounded. Aelle asks his son to give him a warrior's death and Derfel obliges, despite his fear of his prophecy that 'a son will kill his father'. He buries Aelle according to Saxon rites and spares the lives of his men. Lancelot is caught trying to flee the rout, and Derfel forces him to accept a challenge to single combat; despite his cowardice, Lancelot proves to be a competent swordsman, but Derfel defeats him anyway, and has him hanged from a tree.

The power of the Saxons in Britain is broken. Cerdic is forced to retreat with a greatly weakened army and Sagramor conquers several parts of western Lloegyr. Tewdric is known as a saint for his actions at Mynyd Baddon and the Christians credit him with the victory. The old king once again renounces his throne after the battle and Meurig returns to power. The ageing warlord of Gwent, Agricola, is killed during the battle.  Lancelot goes down in legend as the greatest hero of Arthur's retinue, when in truth he was a coward, a rapist, and a traitor.

Part Three: Nimue's Curse
Guinevere tells Derfel that Arthur's price for gaining Gwent's alliegance was giving up his power. As this is what Arthur had always wanted, he agreed and instead leaves Derfel and Sagramor as the leaders of Dumnonia's army: Derfel will command the spears and rule Dumnonia while Sagramor will watch the border with the Saxons. Arthur and Guinevere would leave for Silurian Isca to live in peace. Although Guinevere admits that it was not what she wanted for herself and Arthur, she wanted to be with Arthur. Arthur and Guinevere set up in Siluria, the kingdom which Lancelot abandoned and was divided between Powys and Gwent. They take a warband as Arthur still had enemies. 

As he remains in the lands under Meurig's rule, Arthur becomes one of his tax collectors and soon comes to be known as the Governor of Siluria, as he uses his warband to solve disputes between Silurian chieftains and repel attacks from Demetia. With Cuneglas's death, Powys descends into chaos as several chieftains proclaim themselves king in opposition to the deceased ruler's son, Perddel. The latter manages to retain his throne but he does not have enough men to hold Powys. Eventually, his fractured kingdom is invaded by the Irish king of Lleyn, Diwrnach. Arthur takes his own warriors north to confront this new enemy and, after forcing him from Powys, he tracks Diwrnach on the Dark Road which leads to Ynys Mon and destroys his army. Diwrnach himself drowns during the battle and Arthur successfully reclaims Leodegan's kingdom of Henis Wyren, fulfilling the oath he had sworn to the deceased king.

At the same time, Mordred goes on war raids. First against what remains of the Saxons, reclaiming lands which become Dumnonia's new border in the east, and later in Broceliande against the Franks led by Clovis. In Dumnonia, Derfel attempts to live up to Arthur's legacy by enforcing Mordred's justice with help from Issa, his former second in command who is now a warlord with his own band of warriors. However, his efforts are undermined by Mordred's wife, Queen Argante, and Bishop Sansum, who has become the king's chief counsellor. Both take to undoing the rulings proclaimed by Derfel and the magistrates he appoints in exchange for money. As Mordred continues to fight against the Franks, drawing to him an important army of landless men, many in Dumnonia begin to hope that he will die fighting which would pave the way for a new king to ascend to the throne. Although Arthur (Uther's eldest living son and a well known warrior) refuses the throne, his son Gwydre appears poised to succeed Mordred. A faction begins to develop inside Dumnonia supporting the young man. Making the situation worse for Mordred, his wife is incapable of having children despite frequent visits from the King (and rumours that she has been sharing her bed with palace guards). In contrast, Gwydre and his wife Morwenna (Derfel and Ceinwyn's eldest daughter) have two children, Arthur-Bach and Seren. Gwydre is eager to take the throne because he believes that he can be a better King than Mordred, and his father, Derfel, Sagramor and Issa all appear willing to support him.

A messenger arrives, claiming that Mordred is dying while being besieged by a Frankish army. Derfel tries to avoid a succession issue and goes to Arthur who prepares his army to place his son on the throne. Because Meurig refuses to let the army pass through his kingdom, they must cross the sea. Derfel returns to Dumnonia to find Mordred still alive and learns that he faked his injuries and plans to take revenge on both Derfel and Arthur. Derfel manages to escape with the help of Taliesin, Guinevere's bard, but he learns that Issa has been killed and that Sagramor was defeated. Sansum has also been imprisoned because of his secret attempt to have Meurig seize the Dumnonian throne once Mordred dies. Derfel escapes with the bishop.

Derfel returns to Isca to find Ceinwyn is deathly sick. He is taken to meet Nimue in the far north of Britain who tells that she caused Ceinwyn's sickness and will only remove it if Derfel gives her Arthur's sword and Arthur's son. Nimue plans to use both to complete the ritual to return the Old Gods to Britain. She has also captured Merlin and tortured him into insanity to rip every last secret about being a druid from his mind. In his last moment of sanity, Merlin tells Derfel that he arranged a last trick for him and Arthur as they were the two men he loved most in the world. However, he refuses to lift Nimue's curse, saying that a part of him wants her to succeed where he failed. Derfel, having nowhere else to turn, goes to Morgan, now a Christian, who offers to remove the fever with her old pagan magic only if Derfel will agree to convert to Christianity and serve her husband, Sansum. To complete the spell, Derfel's hand is cut off.

Part Four: The Last Enchantment
Ceinwyn is saved and she converts to Christianity with Derfel, pledging to follow her man wherever he goes. Arthur and his army, carrying Gwydre's banner, travel the sea to Dumnonia but, before they can escape her, Nimue catches up with them. She kills Merlin as a sacrifice to the Sea Goddess, Manawydan, to destroy the fleet. Arthur's army is almost entirely destroyed by the following storm and only his ship makes it to shore. Realizing they can no longer oppose Mordred and his army, the survivors head to Camlan where Merlin has arranged for a ship to take them away to safety. At the last minute, they are joined by Sagramor and the last of his warriors. Mordred comes for Arthur, determined to end the greatest threat to his rule by killing both him and Gwydre. In the brutal battle that follows, Arthur kills Mordred but is wounded during the fight. As the battle seems to turn in favour of Mordred's remaining warriors, an unexpected combatant arrives: Meurig's warriors have come to take Dumnonia's throne for the King of Gwent.

To save Arthur and Gwydre from the latest pretender to the throne, Derfel sends them away on the ship arranged by Merlin along with Guinevere, Morwenna and their grandchildren, Arthur-Bach and Seren. Derfel remains to honour his oath to Morgan and serve Sansum. At the last minute, Ceinwyn decides to stay with him, reminding him of her own oath to always remain with him. As Meurig's forces finish off the remnants of Mordred's army, Nimue arrives to claim Gwydre and Excalibur. However, Derfel casts the sword into the sea , ending Nimue's hopes of bringing back the Old Gods.

Derfel's narration 
The novel also completes the arc of Derfel's narration of the series, as he has been writing the story of Arthur (who was never seen again after Camlan) as a monk under the guise of writing the Gospel in the Saxon tongue.

After the Battle of Camlan, Derfel and Ceinwyn go with Sansum north to a monastery in Powys where Derfel is protected from the bishop's wrath by the protection of King Perddel and, later, of his son, Brochvael. The latter's wife, Igraine, was raised with stories of Arthur as he is portrayed in modern times. She asks him to write his story and provides him with the means to do it, protecting him from Sansum's suspicions. This serves as the thread the story follows.

Despite an apparent conversion to Christianity reflected in his writings, Derfel secretly retains his faith in the Old Gods and, when Ceinwyn dies, he secretly burns her body to allow her soul to join their family and friends in the Otherworld. He writes in his story his own desire to be burnt upon his death as opposed to a Christian burial and hopes that Igraine will grant him his desired funeral.

As the story progresses, the situation in Britain takes a turn for the worse. Despite Meurig's conquest of Dumnonia, Saxons continue to arrive in the weakened Lloegyr, greeted by Cerdic. Rebuilding their forces, the Saxons apparently overrun the combined forces of Gwent and Dumnonia and, as the story is completing, they are threatening Powys. Sansum returns the sword Hywelbane to Derfel so that he can defend their monastery against the approaching Saxons, an act which could lead the reader to believe that Derfel will be killed by the Saxons when they reach them. Derfel secretly hopes that they will and that he will cross the bridge of swords to reach Arthur, his family and their friends in the Otherworld.

Characters
Derfel Cadarn - Protagonist, narrator.
Aelle - Father of Derfel and a Saxon king trying to take Britain. Killed by his son at the Battle of Mynyd Baddon.
Arthur - son of Uther, protector of Mordred.
Ceinwyn - Derfel's common law wife, princess of Powys.
Cerdic - A Saxon king and Aelle's ally in the battle to take over Britain.
Cuneglas - King of Powys and ally of Arthur. Killed at Mynyd Baddon by Cerdic's champion, Liofa.
Cuhlwhch - Arthur's cousin and commander of his guard after he moves to Isca. Killed at the battle of Camlan.
Galahad - A Christian and friend of Derfel.
Guinevere - Princess of Henis Wyren and wife of Arthur.
Issa - Derfel's former second in command who becomes a warlord of Dumnonia after Mynyd Baddon. Killed by Mordred's forces for being an ally of Arthur and Derfel.
Lancelot - Exiled former prince of Benoic now allied with the Saxons against his fellow Britons. Executed by Derfel by hanging after the Battle of Mynyd Baddon.
Merlin – Lord of Avalon, a druid. Killed by Nimue as a sacrifice to destroy Arthur's fleet.
Meurig - King of Gwent, his ambition is to take Dumnonia's throne.
Mordred - King of Dumnonia. Killed by Arthur in single combat during the Battle of Camlan.
Nimue - Priestess, Derfel's former lover who is desperately trying to bring the old gods back to Britain.
Sagramor - Arthur's Numidian commander. Killed at the Battle of Camlan.
Sansum - Treacherous bishop of Dumnonia.
Taliesin - A druidic bard.

Release details
1997, United Kingdom, Michael Joseph , 2 October 1997, hardcover 1st edition
1998, United States, St. Martins Press , 1 June 1998, hardcover
1998, United Kingdom, Penguin Books , 1 October 1998, paperback
1999, United States, St. Martin's Griffin , 16 July 1999, paperback