The Green Knight arrives asking for King Arthur. Everyone is in shock.
The Knight is looking for a challenge. He wants someone to chop off his head then a year later, the Knight will do the same.
The Green Knight starts taunting King Arthur and his men for not accepting the challenge immediately. Arthur then accepts the Green Knights wishes. However, his nephew Gawain steps up to the plate and takes on the Knights challenge.
Gawain then chops off his head causing him no harm. The Green Knight establishes where he lives and expects to see Gawain a year later around Christmas time.
Gawain is lost, but he eventually finds The Green Knights Chapel. Gawain finally comes face to face with him. Then Knight the sings at him. Gawain flinches then is called a coward.
The third time The Green Knight swings at him he didn't flinch. The Knight turns out to be "The Man Of The Castle". Gawain gives the girdle to the man asking for forgiveness. The man forgave him and told him to keep it as token.