During a New Year’s Eve feast at King Arthur’s court, a strange figure, referred to only as the Green Knight, pays the court an unexpected visit. He challenges the group’s leader or any other brave representative to a game. The Green Knight says that he will allow whomever accepts the challenge to strike him with his own axe, on the condition that the challenger find him in exactly one year to receive a blow in return.
Stunned, Arthur hesitates to respond, but when the Green Knight mocks Arthur’s silence, the king steps forward to take the challenge. As soon as Arthur grips the Green Knight’s axe, Sir Gawain leaps up and asks to take the challenge himself. He takes hold of the axe and, in one deadly blow, cuts off the knight’s head. To the amazement of the court, the now-headless Green Knight picks up his severed head. Before riding away, the head reiterates the terms of the pact, reminding the young Gawain to seek him in a year and a day at the Green Chapel. After the Green Knight leaves, the company goes back to its festival, but Gawain is uneasy.
Time passes, and autumn arrives. On the Day of All Saints, Gawain prepares to leave Camelot and find the Green Knight. He puts on his best armor, mounts his horse, Gringolet, and starts off toward North Wales, traveling through the wilderness of northwest Britain. Gawain encounters all sorts of beasts, suffers from hunger and cold, and grows more desperate as the days pass. On Christmas Day, he prays to find a place to hear Mass, then looks up to see a castle shimmering in the distance. The lord of the castle welcomes Gawain warmly, introducing him to his lady and to the old woman who sits beside her. For sport, the host (whose name is later revealed to be Bertilak) strikes a deal with Gawain: the host will go out hunting with his men every day, and when he returns in the evening, he will exchange his winnings for anything Gawain has managed to acquire by staying behind at the castle. Gawain happily agrees to the pact, and goes to bed.
The first day, the lord hunts a herd of does, while Gawain sleeps late in his bedchambers. On the morning of the first day, the lord’s wife sneaks into Gawain’s chambers and attempts to seduce him. Gawain puts her off, but before she leaves she steals one kiss from him. That evening, when the host gives Gawain the venison he has captured, Gawain kisses him, since he has won one kiss from the lady. The second day, the lord hunts a wild boar. The lady again enters Gawain’s chambers, and this time she kisses Gawain twice. That evening Gawain gives the host the two kisses in exchange for the boar’s head.
The third day, the lord hunts a fox, and the lady kisses Gawain three times. She also asks him for a love token, such as a ring or a glove. Gawain refuses to give her anything and refuses to take anything from her, until the lady mentions her girdle. The green silk girdle she wears around her waist is no ordinary piece of cloth, the lady claims, but possesses the magical ability to protect the person who wears it from death. Intrigued, Gawain accepts the cloth, but when it comes time to exchange his winnings with the host, Gawain gives the three kisses but does not mention the lady’s green girdle. The host gives Gawain the fox skin he won that day, and they all go to bed happy, but weighed down with the fact that Gawain must leave for the Green Chapel the following morning to find the Green Knight.
New Year’s Day arrives, and Gawain dons his armor, including the girdle, then sets off with Gringolet to seek the Green Knight. A guide accompanies him out of the estate grounds. When they reach the border of the forest, the guide promises not to tell anyone if Gawain decides to give up the quest. Gawain refuses, determined to meet his fate head-on. Eventually, he comes to a kind of crevice in a rock, visible through the tall grasses. He hears the whirring of a grindstone, confirming his suspicion that this strange cavern is in fact the Green Chapel. Gawain calls out, and the Green Knight emerges to greet him. Intent on fulfilling the terms of the contract, Gawain presents his neck to the Green Knight, who proceeds to feign two blows. On the third feint, the Green Knight nicks Gawain’s neck, barely drawing blood. Angered, Gawain shouts that their contract has been met, but the Green Knight merely laughs.
The Green Knight reveals his name, Bertilak, and explains that he is the lord of the castle where Gawain recently stayed. Because Gawain did not honestly exchange all of his winnings on the third day, Bertilak drew blood on his third blow. Nevertheless, Gawain has proven himself a worthy knight, without equal in all the land. When Gawain questions Bertilak further, Bertilak explains that the old woman at the castle is really Morgan le Faye, Gawain’s aunt and King Arthur’s half sister. She sent the Green Knight on his original errand and used her magic to change Bertilak’s appearance. Relieved to be alive but extremely guilty about his sinful failure to tell the whole truth, Gawain wears the girdle on his arm as a reminder of his own failure. He returns to Arthur’s court, where all the knights join Gawain, wearing girdles on their arms to show their support.