"If any man holds himself...that he dares to stoutly exchange on stroke for another, I shall let him have as a a present this lovely gisarme" (lines 67-70).
A Green Knight asks Arthur to play a game. He says that the game involves someone cutting off his head, then they must allow him to cut off theirs.
Sir Gawain played the game instead of Arthur. He chopped off the Green Knight's head, but he was still alive. He told Gawain that he must come to his Chapel to allow him to chop off Gawain's head, according to the game.
"Come to the Green Chapel, I charge you, and take a stroke the same as you've given, for well you deserve to be readily requited on New Year's morn" (lines 183-185).
"At the end of the day, they will exchange what they have won. While the lord is out hunting, the lady attempts to seduce Gawain. Gawain resists her, however, and on the first two days accepts only kisses, which he gives to the lord at the end of the day in exchange for what the lord has gained in the hunt" (page 216).
On his way to the Chapel, Gawain stays with a lord and lady at a castle. The lord says Gawain and himself must exchange whatever they receive there. The lady made romantic advances on Gawain and kissed him. He refused her and remembered to exchange the kisses with the lord.
The lady continued her advances, and Gawain still refused. Finally, she gave him a green sash as a gift. She said that it would protect him from all harm. Gawain accepts it, but does not exchange it with the lord.
"And she pressed the sash upon him and begged him to take it, and Gawain did, and she gave him the gift with great pleasure and begged him, for her sake, to say not a word, and to keep it hidden from her lord" (lines 241-244).
Gawain wears the green sash and goes to the Green Knight. The Green Knight feints twice, then strikes Gawain with the axe. Gawain is barely harmed.
"I owed you a stroke, and I’ve struck; consider yourself well paid. And now I release you from all further duties" (lines 320-321).
The Green Knight reveals that he was the lord and was testing Gawain. knew his wife gave Gawain the sash, so he knew that Gawain did not exchange the sash as he promised. However, since Gawain only accepted the sash because he wanted to live, he decided that he was worthy. Gawain returns the sash.
"Sir Gawain turned again to Camelot and his lord; and as for the man of green, he went wherever he would" (lines 389-392).