Nice discussion on Sir Gawain and the Green Knight.
In my megalomanical campaign in Dhoesone which I'm
writing I'll use a similar story. Anyhow, the story
as posted missed a few details as I recall the story.
Here's my version.

One day, Arthur and his knights are feasting. Suddenly,
there is a sharp knock on the door and a green knight
on a green horse enters the hall. 'Is this the mighty
Arthur and the Round Table?!', he sneers, 'it looks more
like children playing knight!'
King Arthur rises and suggests the knight test his
might against his own. But Sir Gawain also rose and
said that, as the insult concerned all of the knights
of the Round Table, he would fight the Green Knight.
When he asked the Green Knight the terms of their
songle combat, the Green Knight replied: 'You will
strike at my bared neck now, and in a year, I shall
return the favour at the Green Chapel'. King Arthur
handed Gawain Excalibur, and Gawain sliced the Knight's
head cleanly off. The knight picked up his head, and
said: 'I will see you in the Green Chapel'.
Half a year went by and then Gawain went looking for
the Green Chapel. When the year was almost over,
he still hadn't found it and came to a manor, late
at night.
He was welcomed by the lord and his lady. They told him
the Green Chapel was just two miles away, and asked him
to stay for a day or two. The lord did have one strange
term: he would go out and hunt, while Gawain would rest
to be fit for the ordeal with the knight, and the lord
would give everything he caught to Gawain, but Gawain
would give everything he received during the day to the
lord. And so it was decided.
Awaking the next morning, Gawain felt the lady kiss him,
and then again. He was surprised, and kept the lady com-
pany for the rest of the day [chastly, that is, you AD&D
perverts!]. The lady gave him a girdle. She said: ' This
will protect you from all harm. But do not tell my husband
about it.' And then she kissed him again.
When the lord returned, and gave Gawain his venison,
Gawain kissed him three times. The lord did not look
surprised at all. But Gawain kept the girdle the lady
had given him. After that, they went to sleep.
The next day, Gawain rode to the Chapel. The Green Knight
appeared in the door. 'I see you have kept your promise',
he boomed. 'The Knights of the Round Table always keep
their word', Gawain replied, and bared his neck. The
Green Knight let his gigantic axe come down on Gawain's
neck, but it didn't even leave a scratch. Then he lifted
his axe to strike again. 'Stop!' called Gawain, 'we would
only strike once!' 'That was a year ago,' said the knight,
laughing, 'but you haven't kept your word you gave to me
yesterday!' And while he said this he lifted his visor.
It was the lord from the manor. Gawain understood what the
knight ment and, ashamed, he gave the knight the girdle.
But the knight friendly said: 'You did this because you
promised my wife not to tell me about the girdle. There-
fore, I am not angry. But it does pain me that a Knight
of the Round Table can be so easily tricked by a woman.
Now, let us return to my manor and celebrate today's
But Gawain was not in the mood for a celebration and
returned to Camelot, a bit ashamed and, perhaps, a bit