Plot
Gawain is awakened on Christmas morning in a brothel by his lover, a commoner woman named Essel. He returns to Camelot, following a scolding by his mother Morgan le Fay.
Gawain attends a feast at the Round Table with his uncle the Lord, who invites Gawain to his side. In a tower, le Fay performs a magic rite which summons the mysterious Green Knight who barges into the court as Merlin gives the Lord a look. He states that any knight able to land a blow on him will win his green axe, but must travel to the Green Chapel the following Christmas and receive an equal blow in return. Gawain takes up the challenge. The Knight yields and Gawain, wielding Excalibur, decapitates him. The Knight rises and lifts his severed head, reminds Gawain of the bargain and leaves.
After a year reveling, the Lord reminds Gawain to uphold his end of the challenge. Gawain departs on horseback for the Green Chapel, taking the green axe and a green girdle made by his mother, who claims that no harm will come to him so long as he wears it.
During his journey, Gawain meets a boy scavenging a battlefield littered with dead warriors. The boy directs Gawain to a stream that will lead him to the Green Chapel. He asks for payment and Gawain gives him a single coin. Shortly afterwards, the boy and two others ambush Gawain and steal the axe, girdle and horse, leaving him tied up. Gawain scrambles to his sword and uses it to cut the ropes binding his hands and pursues them.
By nightfall, Gawain arrives at an abandoned cottage and falls asleep in the bed. He is awakened by the ghost of a young woman named Saint Winifred, who asks Gawain to retrieve her head from a nearby spring. He asks what he will receive in return but is rebuffed. He reunites her skull with her skeletal remains and the next morning finds the axe has been returned to him.
Gawain befriends a red fox who accompanies him on his journey where they see some giants. He reaches a castle inhabited by a Lord who informs him that the Green Chapel is nearby, and Gawain accepts his invitation to stay.
The Lord's lady, who resembles Essel, makes seductive overtures towards Gawain. The Lord proposes they exchange what he obtains while hunting with whatever Gawain finds at the castle. The next morning, the Lady presents Gawain with the green girdle, which she claims to have made herself. Gawain accedes to her advances in exchange for it. Gawain flees and encounters the Lord in the forest. The Lord kisses Gawain in return for his Lady's actions, but Gawain does not give him the girdle. The Lord reveals that he has captured Gawain's fox and releases it.
Gawain reaches a stream where a boat is waiting. The fox speaks, imploring Gawain to abandon the quest. Gawain takes the boat to the chapel, where the Knight is seated in hibernation. Gawain waits through the night, and the Green Knight awakens on Christmas morning. As the Knight swings the axe Gawain flinches. The Knight chides him. Gawain kneels for the blow again but at the last moment scrambles away while apologizing on the way out. He finds his horse outside the chapel and rides back home.
Gawain flees back to Camelot. Gawain is knighted and becomes king after the Lord's death. In his reverie, Essel bears his son, but Gawain abandons her, taking the child and marrying a noblewoman instead. His son comes of age and dies in battle. Many years later, Gawain has become a reviled king. With his castle under siege and his wife, daughter, and mother abandoning him, he removes the green girdle, and his head falls from his shoulders.
It is revealed that all that was just a vision. The kneeling Gawain removes the girdle, telling the Knight he is ready. The Knight praises Gawain for his bravery, drags his finger across Gawain's throat and points past him, stating "Now, off with your head". He smiles kindly.