At the Christmas celebration in Camelot, and huge Green Knight appears with an axe, saying that he will submit to a blow from the axe if he can repay the blow in a year and a day. Gawain agrees and chops off the knight's head. The knight grabs his head, reattaches it, and rides off.
The next year, Gawain sets out to receive his blow, and finds a castle nearby the Green Knight's chapel. The lord and lady welcome Gawain, and promise an exchange of gifts. The lord goes hunting.
The lady of the castle tries to woo Gawain. She offers a deer for one kiss from him, a boar for two, and a fox for three. Gawain consents, and is also persuaded to take a magic green girdle that is said to protect the wearer from all harm.
Gawain sets out for the Green Knights chapel, accompanied by a servant of his host. The servant urges him to turn back, and tells Gawain that he will not betray him. Gawain refuses however, and rides to the Green Knight's chapel.
Gawain arrives at the chapel and finds the Green Knight waiting. As the knight prepares the strike, Gawain flinches, causing the Green Knight to mock him. Gawain is angry, but steels himself and tells the knight to swing again.
Gawain doesn't flinch the second time, but the knight only nicks his should instead of loping of his head. He then tells Gawain that this was all a test, one that Gawain passed up until he gave in to fear and took the girdle that the lady offered him. Gawain returns the girdle, and the two knights go back to the castle to enjoy the festivities.