"Thou shalt die," said Sir Gawaine, "for slaying of my hounds."
"I will make amends," said the knight, "unto my power."
Sir Gawaine would no mercy have, but unlaced his helm to strike off his head, when at that instant came his lady out of a chamber. She fell upon her husband just as the blow descended, and so Sir Gawaine smote off her head by misadventure, and the knight was saved.
"Alas!" said Gaheris, "that is foul and shamefully done; that shame shall never depart from you. Ye should give mercy unto them that ask mercy, for a knight without mercy is without honour."
Sir Gawaine was so astonished at the death of the fair lady that he knew not what he did, and he said unto the knight, "Arise, I will give thee mercy; and go thou unto King Arthur, and tell him how thou art overcome by the knight that went in the quest of the white hart."
"I care not for mercy now," said the knight, "for thou hast slain my lady that I loved best of all earthly things it matters not whether I live or die."
Then Sir Gawaine went into the castle and made ready to rest there all night.
"What will ye do?" said Gaheris; "will ye unarm you in this country? Ye may believe ye have many enemies here."
He had no sooner said that word than there came four knights well armed, and anon they made Sir Gawaine and Gaheris yield themselves as prisoners, in spite of the brave battle wherein Sir Gawaine was sore wounded in the arm.
Early on the morrow there came to Sir Gawaine in the prison one of the ladies of the castle, and said, "Sir Knight, what cheer?"
"It is your own fault," said the lady, "for ye have done a passing foul deed in the slaying of the lady, which will be great disgrace unto you. Be ye not of King Arthur's kin?"
"Yes, truly," said Sir Gawaine. "My name is Gawaine, and my mother is King Arthur's sister."
"Ah, then are ye nephew unto King Arthur," said the lady, "and I shall so speak for you that ye shall have conduct to King Arthur, for love of him."
Then anon they delivered Sir Gawaine under this promise, that he should bear the dead lady to the court, the severed head hanging about his neck. Right so he rode forth unto Camelot, and Merlin made him tell of his adventure, and how he slew the lady, and how he would give no mercy unto the knight, whereby the lady was slain. Then the King and the Queen were greatly displeased with Sir Gawaine, and by ordinance of the Queen there was set a quest of ladies on Sir Gawaine, and they ordered him for ever while he lived to be with all ladies, and to fight for their quarrels; and that ever he should be courteous, and never refuse mercy to him that asketh mercy. Thus was Gawaine sworn upon the four Evangelists that he should never be against lady nor gentlewoman, except if he fought for a lady and his adversary fought for another.