Sir Gawain and the Green Knight is a late 14th century metrical romance recorded in a manuscript containing a number of other pieces of an altogether more Christian orientation, which are linked by a commonality of dialect usage. The dialect is the West Midland form of Middle English. The core of the story, however, is far older and embraces many elements central to Celtic mythology, although it is also coloured by events of the time, chief amongst which were the Black Death.
The manuscript, Cotton Nero A.x is in the British Museum. The first modern edition was published by J. R. R. Tolkien and E.V. Gordon in 1925.
In the story, Gawain, a knight of King Arthur in Camelot, becomes a guest at Hautdesert Castle. During this sojourn, three hunts take place, and are paralleled by three temptations laid before Gawain by the Green Knight's wife.
The story, set in verse, begins at King Arthur's court at Camelot on New Year's day. As Arthur's court is feasting, a stranger, the gigantic Green Knight, on horseback and armed with an axe, enters the hall and lays down a challenge. One of Arthur's knights may take the axe and strike a single blow against the Green Knight, on the condition that the Green Knight, if he survives, will return the blow one year and one day later. Sir Gawain, the youngest of Arthur's knights, accepts the challenge and chops off the giant's head. The Green Knight, still alive, picks up his own head, reminds Gawain to meet him at the Green Chapel in a year and a day, and rides off.
Almost a year later, on All Hallows Day, Sir Gawain sets off in his finest armour, on his horse Gringalet, to find the Green Chapel and complete his bargain with the Green Knight. His shield is marked with the pentangle, a symbol of Biblical origin, which is to remind him of his knightly obligations. The journey takes him from the isle of Anglesey to a castle somewhere in the West Midlands. Gawain meets the lord of the castle and his beautiful wife, who tell him that the Green Chapel is close by, and suggest that he stay with them.
The lord, before setting off on a day's hunting, offers a deal to Sir Gawain. The lord will give Gawain whatever he catches, on condition that Gawain gives to the lord, without explanation, whatever he might gain during the day. Gawain accepts. That night, while the lord is still away, the lady of the castle visits Gawain's room and tries to seduce him, claiming that she knows of the reputation of Arthur's knights as great lovers. Gawain, however, keeps to his promise to remain chaste until his mission to the Green Chapel is complete, and yields nothing but a single kiss. When the lord returns with the deer he has killed, he hands it straight to Sir Gawain, as agreed, and Gawain responds by returning the lady's kiss to the lord. According to the lord's bargain, Gawain refuses to explain where he won the kiss.
On his second night, Gawain again receives a visit from the lady, and again politely refuses her advances. Next day, when the lord returns, there is a similar exchange of a hunted boar for two kisses.
On his third night, when the lady visits his chamber, Gawain maintains his chastity but accepts a silk girdle, which is supposed to keep him from harm, as a parting gift. The next day, the lord returns with a fox, which he exchanges with Gawain for three kisses.
The next day, Gawain leaves for the Green Chapel, with the lady's silk girdle hidden under his armour, and accompanied by a guide from the lord's castle. Leaving the guide, who is afraid to approach the Green Chapel, Gawain finds the Green Knight busy whetting the blade of an axe in readiness for the fight. As arranged, the Green Knight attempts to behead Gawain, but after three attempts Gawain remains only slightly injured, the third blow barely cutting his neck. The Green Knight then reveals himself to be an alter ego of the lord of the castle, Bertilak de Hautdesert, and explains that the three axe blows were for the three occasions when Gawain was visited by the lady. The third blow, which drew blood, was a punishment for Gawain's acceptance of the silk girdle.
The Green Knight explains that Gawain's trial was arranged by Morgan le Fay, mistress of the wizard Merlin and now a guest at Hautdesert castle. The two men part on cordial terms, Gawain returning to Camelot. There, Sir Gawain recounts his adventure to Arthur and explains his shame at having partially succumbed to the lady's attempts, if only in his mind. Arthur refuses to blame Gawain and decrees that all his knights should henceforth wear a green sash in recognition of Gawain's courage and honour.