Yvain by Chrétien de Troyes is the story of a knight who seeks to regain his honor after he breaks a promise. It was originally written in French and was likely composed in the second half of the twelfth century.

The story starts in King Arthur's court. Calogrenant, a knight, tells a story of a time when he was bested by another knight. The incident took place by a magic spring with water that, when poured, conjured an immense storm. He says that the encounter brought great shame to him; he's mocked by another member of the court for his folly.

Yvain, hearing the story, decides that he is going to make things right. King Arthur wants to see the things that Calogrenant described and offers to let other knights accompany him. Yvain sneaks out ahead of them, wanting to complete the quest he said he would undertake on his own. Yvain arrives at the spring, battles the knight, and then pursues the seriously wounded man when he enters a castle, where Yvain is trapped.

If not for a maid, Lunete, who gifts him a magic ring that makes him invisible, Yvain would be killed by the men who search the area for him. The knight dies, leaving his wife a widow. When Yvain sees Lady Laudine, the knight's widow, he falls in love. Lunete helps convince Lady Laudine to take a new husband; she decides to do so and accepts Yvain's proposal.

When King Arthur's group arrives at the spring and pours the water on the ground, Yvain responds. His armor conceals his identity. He battles the man who mocked Calogrenant and him at court and wins. Everyone returns to Yvain's new estate for fun and games. However, after a week, Sir Gawain convinces Yvain to go with King Arthur and the others to participate in the tournaments being held. Lady Laudine says he can go, as long as he returns within a year. She also gives him a ring that will keep him from harm—if he keeps thinking of the woman he loves.

Yvain does so well at the tournaments that he doesn't return as promised. He only remembers his promise when she sends someone to collect the ring and tell Yvain off for being a liar. Yvain doesn't take this well. He goes into the forest and lives, naked and starving, until a hermit finds him and takes care of him with food and water. When the Lady of Noroison finds Yvain sleeping nude, she and her ladies heal him with a magic cream. He helps the Lady of Noroison with a problem she's having with a man who is invading her lands—then leaves, even though she offers marriage.

Yvain embarks on a series of adventures, including battling a fire-breathing serpent. He saves a lion from the serpent, and the lion begins to travel with him. Next, he slays a giant who holds a baron's four sons captive. Yvain asks after this to be known as the Knight with the Lion. He then saves Lunete from being burned alive by Lady Laudine, who was convinced by a courtier that she acted with false intentions when she convinced Lady Laudine to marry Yvain. He also fights on behalf of one of the daughters of the departed Lord of Noire Espine, who is being cheated of her inheritance by her older sister. He wins against Sir Gawain, who, upon recognizing Yvain after an entire day of fighting, gives in. However, Yvain doesn't agree with that decision and tries to let Gawain win. King Arthur then decides that the young...