"Yonec" is one of the Lais of Marie de France, written in the twelfth century by the French poet known only as Marie de France. Yonec is a Breton lai, a type of narrative poem. The poem is written in the Anglo-Norman dialect of Old French in rhyming couplets of eight syllables each. This lai tells the story of a woman who seeks to escape a loveless marriage, and of the child born from the love that she found elsewhere.
The lord of Caerwent, a rich old man, marries a beautiful young woman. He fears that she will be unfaithful to him, so he imprisons her in a tower and assigns his aged sister to watch over her. As the years go by, she laments her situation and stops taking care of herself, making her beauty fade away. One day, she cries out to God, wishing that she could experience a romantic adventure as she has heard in fairy tales. Suddenly, a dark bird resembling a goshawk appears at her window. The bird transforms into a handsome knight named Muldumarec. Muldumarec declares his love for her and reveals that, while he has loved her from afar, he could only approach her once she had called for him. The woman refuses his advances unless he can prove that he was not sent by the devil to lead her astray. Muldumarec says that he is a Christian, and as proof of such, he assumes the woman's shape and receives the Eucharist.
When the rich lord is away, the knight arrives by the window, in the same way he first appeared. The woman glows with her newfound love. The other people of the household become suspicious of her renewed beauty and put her under discreet surveillance. When the jealous husband learns of the shapechanging knight, he surrounds the window with iron spikes. The next time the knight arrives, he is mortally wounded. He tells the woman that their unborn child, whom she is to name "Yonec", will grow up to avenge their deaths. The knight flies away, and the woman hurls herself from the window and follows a trail of blood to a city made of silver. After passing through a succession of rooms, she eventually finds the knight on his deathbed. He gives her a magic ring that will make her husband forget about her infidelity. He also gives her his sword. As the woman flees the city, she hears the bells tolling for her lover's death.