Marie informs us she would be remiss to omit the lay of Bisclavret, a werewolf from the old days of Brittany. She speaks of the werewolf curse as something that "often used to happen."
She begins her tale by introducing a noble and handsome baron (Bisclavret) who is loved by all in his home realm of Brittany. He lives with his beautiful and loving wife, and all is well between them except for one thing: each week, the baron disappears for three days, and nobody knows where he goes. Finally, she is driven to confront him on one of his returns. She tells him she has a question that she fears to ask, and he promises to tell her anything she would know. However, when she poses her question about his disappearance (most frightened he might reveal the existence of another lover), he falters and asks her to withdraw the query, since the answer meant "great harm would come to [him] and [he] shall lose [her] love and destroy [himself]."
She perseveres with her question, and ultimately convinces him to reveal the truth: each week, he becomes a werewolf. Though she lets on no sign of concern, she immediately begins to question him, learning in the process that he must unclothe himself to turn and that he must hide his clothing in order to facilitate his transformation back to man. Without his clothes, he would "remain a werewolf forever." He doesn't want to tell her where he hides his clothes, but when she insists he reveals his hiding place in a hollow rock next to an old chapel deep in the woods.
Marie then reveals the wife's true feelings – she is disgusted and no longer "wished to lie with him." She begins to plot how to rid herself of the burden, and to that end contacts a knight who had always wanted her as a lover, but whose advances she had repudiated. She offers her "love and body" if he will steal Bisclavret's clothing. The knight agrees, and Bisclavret is seen no more. The lady marries the knight, Bisclavret's friends search for him a while, but when he is not found, all are forced to move on.
A year passes, until one day when the king is out hunting in the forest where Bisclavret disappeared. The hunting dogs come across the werewolf and the hunters spend their day in pursuit of him, until they are upon him and about to kill him. However, Bisclavret, instead of fighting, rushes to the king and begs for mercy by kissing the lord's feet. Though frightened, the king is equally impressed with the obvious intelligence and humility in the creature, and calls off the hunt.
The king brings the wolf back to his castle, where the wolf becomes a favorite amongst all. The king orders it protected, and the wolf loves the king in turn. All of his men feed and guard it, and Bisclavret even sleeps each knight amongst the knights. They have never seen anything quite like him.
All is well until the king holds court and summons all of his vassals, one of whom is the knight who had married Bisclavret's wife. When the wolf sees the man, he launches an attack upon him, attempting to tear him apart. Bisclavret retreats when threatened by the king, but continues to attempt attacks until the festival has ended, which prompts much suspicion amongst the king's men that the knight must have harmed the usually docile wolf in some way to inspire such hatred.
Soon after, the king returns to hunt in the woods, and Bisclavret accompanies him. That night, they take lodging in the area and when Bisclavret's wife hears of this, she decides the next day to visit the king and present a gift to him. When the wolf sees her approach, he launches at her and tears off her nose! He is barely restrained and is on the verge of being killed when a wise man points out to the king the connection between the two people who the wolf has attacked (they are married), and also that the woman was the wife of the much-loved Bisclavret who disappeared some time before. The wise man suggests the king question the wife, which he agrees to. Under torture, the now noseless wife confesses all that she has done, as well as her belief that the wolf is her husband.
The king demands the woman return the clothes, which she does. However, the wolf barely acknowledges them, until the wise man points out that he is likely humiliated to change in front of the king. Thus, the latter puts the wolf in his own bedroom with the clothing, and returns soon after to find the human Bisclavret asleep. They are joyfully reunited, and the king restores to Bisclavret his lands, while also banishing the wife and her new husband. Marie tells us that the latter pair had several daughters in their day, all of whom were born lacking noses.
Marie ends her lay insisting that this story is true, and that it is immortalized in the lay.
This lay is unique in its use of the extended metaphor of the werewolf. While the metaphor is straightforward enough – the wolf represents our beastly, perhaps sexual side – its implications are more skillfully handled in the lay than such a simple interpretation suggests.
To best understand how Marie uses the symbol, consider the contrast between a love based in loyalty and one based in selfishness and lack of understanding. Bisclavret's wife is very much guilty of the latter. It calls to mind Marie's assertion in "Guigemar" that "a loyal partner, once discovered, should be served, loved and obeyed." She paints their relationship as initially strong and loving, and yet makes effort to describe the wife in physical terms, while her husband is described in terms of his nobility and popularity as well.
Certainly, we can empathize with the woman's horror at learning her husband turns to a beast. But her disgust is strictly characterized as a physical one. She shows no concern about his well-being, but instead does not want to "lie with him" any more. He makes an effort to hide this side of himself from her, so much so that he discourages her from attempting to learn about it. And yet she is not affected by his shame over the change; all that she can see is that the fact that he does change.
The irony is of course that she herself has a beastly side, and gives into that beast in order to vanquish her connection to his inner beast. She might not physically transform, but her sense of herself as just a sexual being parallels his animal nature as a werewolf. Once she learns about his curse, she becomes immediately vindictive and uses her body as a tool – Marie tells us she has never loved the knight she allies with, but uses her body to attract him and get him to do her dirty work. There is a wonderful joke after she offers the knight her body and love – "he thanked her warmly and accepted her pledge." They are both self-involved people who are willing to exploit their physical desires, even at the expense of someone else's happiness. This, indeed, shows their own animal side. It is telling that Bisclavret's revenge on his former wife does not involve torture or death, but rather the bizarre de-nosing. The point here is that he wishes to wound her vanity, the vice she was too obsessed with.
All of this contrasts with the mature and balanced way that Bisclavret manages his own beastly nature. He has an appropriate sense of shame about it: where his wife immediately prostituted herself to her adorer, Bisclavret recognizes this part of himself as unfit for human eyes. He keeps his curse a secret, and even at the end of the lay, refuses to change into his clothing in front of others. He has a great understanding that we must first accept our beastly nature, and then endeavor to hide it.
By accepting it and trying to avoid it, he shows himself capable of an admirable love based in loyalty. This love is manifest both in the trust he unwisely shows his wife, and in his devotion to his lord. Because of the latter, he is equally loved in turn and earns the king's love even when the king doesn't recognize him behind the fur. As a wolf, he cannot hide his beastly nature; however, he can endeavor to transcend it, which he does through his docility and sweetness in the king's court.
Marie's ultimate message, on top of her usual condemnation of selfish love, is about moderation. She'd have us realize that each of us battles with an inner beast, and yet the wisest and most virtuous of us attempt to make that beast subservient to our reasonable side. When the werewolf first approaches the king, the king is terrified but can also sense that this beastly nature has been subsumed behind a reasonableness that is begging for mercy. Because he is able to prize loyalty over selfishness, and to accept his beastly side and address it maturely, Bisclavret ends up okay. On the other hand, his wife refuses to question her own selfish vanity and as a result ends up banished and sire to a legion of noseless heirs.
Lastly, we see Marie's authorial interjection at the end of the lay, when she stresses the truth of the tale. Naturally, many could be led to recognize the fairy tale pattern at work in the lay, and yet Marie refuses to allow her story to be attributed to that. Is she trying to stress the truth of the poem's meaning, just being playful, or trying to defend herself against those who would accuse her of making up stories? The medieval tradition at the time would not have frowned upon using classical archetypes, so it is an interesting assertion for her to make.