Igraine’s sister, Viviane (The Lady of the Lake), arranged a marriage for her and sent her away from Avalon to live in Cornwall when she was fifteen. She is lonely there, and her much-older husband is usually at war. She has a daughter, Morgaine, for company, but that is it.
Five years after her marriage, Viviane visits Igraine. After all the misery Igraine has gone through for her marriage to Gorlois, Viviane tells her that she is going to be the mother of the high king, the first man to unite Britain in history. However, the father will not be Gorlois. Igraine wants nothing to do with the idea. She is married to Gorlois, and she will not completely abandon her life for the sake of Viviane’s whims a second time.
Igraine travels with Gorlois to Londinium when the counsel to decide on the next king his held. Igraine meets Uther, who is ultimately chosen to be king, and they both immediately feel that they have known, and loved, each other in past lives. Although they do not do anything that they shouldn’t, Gorlois accuses Igraine of cheating on him, and he takes her back home and essentially holds her captive. Uther asks Gorlois to give Igraine to him, but Gorlois refuses and goes to war against Uther. Igraine uses the Sight to send a message to Uther warning him that Gorlois is going to attack, so Uther uses the warning to prepare and strike back. Uther kills Gorlois, takes his armor, impersonates him, and goes to Igraine. The next morning, Gorlois’ body is brought to the castle and Uther comes down from Igraine’s chamber. Uther and Igraine are married.
Morgaine and Arthur grow up together, ignored by their parents who are too wrapped up in each other. Eventually, Viviane takes Morgaine to be fostered in Avalon and Arthur is sent to be raised by Ectorius, one of Uther’s allies. Morgaine became a priestess, and Arthur was raised modestly without the adoration of being a king.
One day, Morgaine’s cousin Lancelet visits. She is immediately attracted to him, and he to her. However, a girl manages to get lost in the mists between Avalon and Glastonbury. Lancelet is drawn to her instead, and the girl, Gwenhwyfar, is drawn to him but is afraid of Morgaine, whom she thinks is a witch. Morgaine leads Gwenhwyfar back through the mists, but her romantic afternoon with Lancelet is over.
Viviane sends Morgaine to make the “Great Marriage,” a fertility ritual with a masked warrior. However, when they wake up the next morning she finds that it is Arthur, her half-brother. Morgaine becomes pregnant, and she leaves Avalon because of how mad she is at Viviane. She gives birth to her son, Mordred, at the home of her Aunt Morgause. Morgause’s husband, Lot, wants to kill the child so that his sons will be next in line for the throne of the High King, but Morgause finds out who the father is and decided to raise him as her own son so that he can become king, but will do whatever she wishes him to do. Morgause also takes steps to ensure that Gwenhwyfar will never bear children.
Morgaine goes to Camelot and becomes a maid for Gwenhwyfar. They are mostly peaceful, but their old prejudices still get in the way. Gwenhwyfar ignores her prejudices long enough to ask for a fertility charm so that she can get a son, but the charm makes Arthur ask Lancelet to join him and Gwenhwyfar in a threesome, so that if Gwenhwyfar does get pregnant they will never know for sure who the father was. Gwenhwyfar does not get pregnant,so she blames her infertility on Arthur’s allegiance to Avalon. She claims that God would not reward Arthur’s allegiance to heathens with a child, so Arthur must renounce Avalon in order to get an heir. Arthur complies. Morgaine could not keep the spirit of Avalon alive in Camelot, so Avalon is becoming harder and harder to reach as time goes on and it loses its connections to the outside world.
Morgaine arranges a marriage between Lancelet and Gwenhwyfar’s cousin, Elaine. Gwenhwyfar is outraged. When a very old king, Uriens, asked Arthur for a wife, Gwenhwyfar steps in and suggests Morgaine. When Morgaine is asked if she would like to “live in North Wales,” she thought she was agreeing to marry Uriens’ son, Accolon. She didn’t figure out what was happening until too late, and she married the father instead.
While in Wales, Morgaine retrains herself to work the magic of Avalon and starts training Accolon (who is also her lover) to challenge Arthur because of his desertion of Avalon. When the challenge happens, Accolon and Uriens both die, but Arthur lives. Morgaine goes to Avalon to recuperate.
Mordred reaches adulthood and goes to live at Camelot. He earns Arthur’s trust and reveals his parentage, which enrages Gwenhwyfar. Gwen makes Arthur confess his “sin” of participating in the great marriage, and he begins penance without letting the general public know why. Gwenhwyfar and Lancelet finally begin their affair shortly after this.
Morgaine and a fellow priestess, Raven, journey to Camelot years later because a vision told them to. They find that their most holy objects have been stolen by the high priest, Kevin, and given to the Christians. The goddess takes over Morgaine’s body and the famous sighting of the Grail ensues. Avalon plans revenge on Kevin for his betrayal. They send Nimue, a girl who has not been seen by any man since a young age, to Camelot. She makes Kevin love her, and then she uses a spell to bring him to Avalon, where he is executed and his body is put inside the trunk of a tree that was split by lightning at the moment of his death. However, Nimue also fell in love with him, so she drowned herself after betraying Kevin to his death.
Morgause and Mordred raise a posse to reveal Gwenhwyfar’s affair with Lancelet so they can lower Arthur’s popularity, and Mordred can challenge him. Gwenhwyfar and Lancelet escape, but they realize they cannot stay together. Gwenhwyfar goes to a nunnery, and Lancelet returns to help Arthur fight Mordred.
In the final battle, most of the knights are killed. Mordred is killed by Arthur, but Arthur is mortally wounded by Mordred as well. Morgaine brings him to Avalon in hope to nurse him back to health, but he dies while parting the mists.
Morgaine stays on Avalon for many years, but she ventures to visit Viviane’s grave on Glastonbury one day. She sees people worshipping St. Mary, and she realizes that the goddess is still alive in the world, even though Avalon is not.