While King Arthur is having a New Year's celebration, The Green Knight shows up and proposes a challenge to any brace Knight, and King Arthur offers himself. "Now has Arthur his ax, and the haft grips, and sternly stirs it about" (105-106).
Before King Arthur can go through with the challenge, Sir Gawain comes in and accepts the challenge himself. "Would you grant me this grace, said Gawain, to the king, to be gone from this bench and stand by you" (117-118).
Sir Gawain successfully removes the Green Knight's head. "And he rose up readily, and reached him with speed, bows to his lord, lays hold of the weapon..." (141-142).
A year and a day later, Sir Gawain starts his journey back to meet the Green Knight, where he will let the Green Knight have on swing on him with his ax. "He puts his heels to his horse and picks up the path" (259).
The Green Knight attempts to cut off Sir Gawain's head, but is unsuccessful and only leaves a mark. "But Gawain at the great ax glanced up aside as down it descended with a death-dealing force" (359-360).
Sir Gawain returns to King Arthur with the Girdle he won and they celebrate his success and victory over the Green Knight. "and I give you sir, this girdle that is gold hemmed and green as my garments, that, Gawain, you may be mindful..." (484-486).