The Once and Future King Book 3, Chapter 7

Lancelot goes on many quests to escape Guenever. One day, he comes upon a wicked knight named Sir Carados, who has taken Gawaine prisoner. Lancelot offers to fight for Gawaine, and fairly easily kills Sir Carados. They ride off, and Lancelot joins his cousin Lionel in other quests. But soon Lionel is captured by Sir Turquine, a brother of Sir Carados, who likes to keep people captive, beating them. Meanwhile, Lancelot is captured by four witches, including Morgan le Fay. They keep him prisoner and tell him that although he and Guenever are having an affair, he must choose one of them for his mistress. He denies the affair, and says he will not choose any of them. A young maiden in the castle promises to help Lancelot escape if he will fight with her father in a coming tournament. He agrees to meet her and her father, but gets lost on the way and goes to sleep in a strangely deserted building in the middle of the forest. He wakes up when the owner of the place comes home, and they fight but soon make up, and Lancelot brings the man (Sir Belleus) to be a knight at Arthur's Round Table. He then wins the tournament for the young maiden's father. He meets a woman in the forest afterward who tells him about Sir Turquine (though she does not know Turquine has captured Lancelot's cousin.) Lancelot goes to fight Turquine simply because he believes in Arthur's ideas about Might not making Right. Turquine is a great fighter, but Lancelot beats him, and rescues, among others, Gaheris.