The Green Knight enters Arthur's castle and immediately makes fun of how unimposing its inhabitants are, then challenges the knights to cut off his head with the Green Kight's own axe. Arthur, angry, says he will do it.
"...and here sit young men...I will abide the first blow [of the ax], bare-necked as I sit" (66-72).
Gawain steps in front of Arthur and claims that HE will take the shot at the Green Knight. The other knights agree.
"Let the King step down and give Sir Gawain the game" (146-147).
"'I beseech you, Sire, let this game be mine'" (123-124).
Although Gawain slices off the Green Knight's head, the latter is able to walk away, beheaded, with his own head in his hands. The Green Knight reminds Gawain of his promise: at the end of the year, the knight will slice Gawain's neck.
"'Look that you go, Sir Gawain, as good as your word, and seek till you find me... as you’ve sworn in this hall to do, in the hearing of the knights.'" (172-174)
Gawain travels through lands to fulfill his promise. During this time, he finds a castle, which he stays in upon the lord's request. The lady tries to seduce Gawain and give him gifts. He refuses until the third day, when he takes a green sash that will make him invincible in battle.
"For the man who goes to battle in this green lace...no man under Heaven can hurt him" (223-225).
After leaving the Lord and Lady, Gawain finally reaches the Green Knight. When Gawain first bows his head to take the strike, he flinches before the axe is even swung, which causes the Green Knight to claim he is a coward. The second swing hits its unflinching target; however, the sash protects his neck, and he leaves with only a scratch.
"But you! You tremble at heart before you’re touched! I’m bound to be called a better man than you, then..." (259-260).
Gawain notes that the deal is sealed. The knight remarks at Gawain's courage and general loyalty to the deal and reveals that it was his wife who gave Gawain the sash. While taking it technically broke the deal, the Green Knight understands Gawain's love of life. The Green Knight then invites Gawain to a feast, which he refuses. They part merrily.
"Whatever harm I've had, I hold it amended since you're confessed so clean...I consider you polished as white and as perfectly clean as if you had never fallen since first you were born" (367-371).