Marie closes her collection with "a very old Breton lay" about a brave and courtly knight who once lived named Eliduc. She gives a basic summary to begin, about how Eliduc had a happy, loyal marriage with his wife Guildeluec but later fell in love with a maiden named Guilliadun. The lay was once named after him, but was later renamed after the ladies. (Nevertheless, Marie uses his name as her title.)
Eliduc is loved dearly by the King of Brittany, who trusts him as main guard of his lands. Because of this boon, Eliduc is granted many privileges including the right to hunt where he pleases. His favored position inspires envious enemies to slander him before the king, who angrily banishes him despite the lack of formal accusation. The king will not hear his attempts at defense, so Eliduc decides to travel to Logres in hopes the king will calm down. He takes ten knights only, and though his wife, with whom he has a trusting relationship, laments his leave, she is comforted by his promise to be faithful to her.
When Eliduc arrives in the land of Tontes, he finds it in the grips of war. An old lord has long refused to give his daughter in marriage to any suitors, and so another powerful lord is making war for her. The enemy has surrounded the old lord's castle, which gives Eliduc a chance to prove himself and find a new lord to patronize his services. He informs the king that he will gladly fight for him, an offer the king accepts. Eliduc is given fine lodgings in the town, and Eliduc forbids his men to take too much hospitality for the first 40 days.
Soon after they arrive, the enemy assaults the town and Eliduc gets to work. When the knights of the town see Eliduc ready to fight, they all mount up as well. He asks them if there is a narrow pass that he can use to ambush the enemy, and he is told of a path that the enemy would have to pass while retreating. The plan becomes to let the enemy take some spoils from the city, so that they will believe themselves victorious and then be an easy ambush from the passage on their return.
The plan works masterfully, and Eliduc leads his new army to destroy the enemy and take many spoils. However, as they return, the king, who has grown suspicious that Eliduc is working against him, sees the larger ranks and thinks he is being attacked. He orders the town to bombard the approaching victors, but a messenger arrives first and defuses the potential battle. The king is overjoyed to learn the truth, and when Eliduc turns over the prisoners, the king agrees to retain Eliduc as vassal for a year.
During this period, the king's daughter, Guilliadun, hears of Eliduc's valour, and so asks him to visit her. When he does, behaving reservedly in deference to his wife (whom he nevertheless does not mention), they speak for a while and she falls in love with him, in the moment going pale and sighing from the emotion. Eliduc is troubled by the sign of her affection, and forces himself to remember Guildeluec.
Guilliadun, however, is terribly stricken and cannot sleep, she wants him so badly as her lover. She confesses this to her chamberlain, and says she will die without him. The chamberlain urges discretion, and suggests a test: she should send to him a gift, and if he receives it gladly, then she will have reason to believe he loves her as well. She is doubtful whether such a test will prove anything, but acknowledges it will provide some indication of his character. She sends the chamberlain off with a gold ring and girdle as gifts, meanwhile lamenting her poor fortune to love someone of whom she knows so little.
Eliduc receives the gifts without any clear sign, wearing both gladly. The chamberlain, confused by the response, tells the lady, "The knight is not fickle…He knows well how to conceal his feelings." The chamberlain is nevertheless optimistic, since he received the gifts, and he convinces the lady to learn more about Eliduc and attempt to win him to her favors during Eliduc's year of service to her father.
She does not know that Eliduc nurses his own pain, since he has fallen in love with her too but is guilt-ridden with remembrance of his wife. He promises never to pursue her love, yet does want to see her and so visits the king, where he is introduced officially to her. There, they sit apart, "both caught in love's grip," quiet until she confesses she wishes to be his wife. He thanks her for it, and tells her he is only there for a year – she gladly tells him he will have that time to decide what to do about her offer. So do Eliduc's days grow happy, since he can be in love without being forced to act on it. During this time, he continues to defeat the king's enemies, in the process freeing the entire realm.
Eliduc's original king, meanwhile, is having trouble with his own enemies, and has sent messengers to find the knight and beg his return. He has banished those who slandered Eliduc, and wishes his pardon. When Eliduc learns of his lord's trouble, he is distressed. He knows he must return, especially since he has rid his current lord of any potential enemies, but worries that if he leaves Guilliadun (who still does not know about Guildeluec), then she will possibly die. They have still never done anything but talk, and he knows he cannot marry her without forsaking his Christianity. He feels as though he has behaved terribly towards her, and decides he will explain the situation to her.
Eliduc first takes leave of the king, who is sad and offers the knight much wealth to entice him. However, Eliduc takes only a moderate amount and promises that he will gladly return to aid the king should he ever find himself in trouble again. The king is happy with this, but the meeting with Guilliadun goes less well. She faints and, distraught, he kisses her back to consciousness and then promises to do as she wishes. She wants to be taken with him, threatening to kill herself otherwise, but he convinces her a better plan is for her to set a date by which he promises to come back for her.
On his return, Eliduc is treated warmly by all, especially his faithful wife. However, his sadness is palpable, and his wife fears it is because she has been slandered and he no longer trusts her. He convinces her this is not so, but lies that his lord across the sea will need him to return as quickly as possible. Eliduc helps his original lord rid himself of enemies speedily, and then sets sail again for his beloved Guilliadun.
When he lands back in Tontes, he sends word to her that she should sneak from the town that night, so he can fetch her and bring her home with him, now that his term of commitment to her father has expired.
That night, they are lovingly reunited and they set sail again immediately for Brittany. The sailing is easy for a while, but as they approach home, a terrible storm begins and blows them back out to sea. As the storm worsens and many begin to fear they will die, one sailor lambastes Eliduc for bringing this curse upon them by offending God with his extra-marital dalliance. The girl, hearing for the first time of a wife, falls into a dead faint and Eliduc throws the solider overboard.
Once on land, the girl is seemingly dead, but Eliduc will not let her go. Being a daughter of a king, she deserves a royal burial but he does not know how to arrange this. He remembers that, in the woods near his home, there lives a hermit in an old chapel, and decides he will bury her in the chapel and then donate much land to build an abbey there so she is buried in a sacred place. They travel to the chapel to find that the hermit had died merely days before. He leaves her limp body there, promising he will consult others about how best to consecrate the place before burying her.
He arrives home and is even more distraught than before, which concerns his wife. Each day after hearing mass, he heads to the chapel where he bemoans the tragic fate of Guilliadun, and so Guildeluec sends a spy to find out what he is doing. The spy hears his wailing and sees him exit, and reports this to her. She is naturally confused, since she does not believe the hermit's death would cause him such grief.
One day, when Eliduc goes to visit the king, Guildeluec investigates and finds the maiden's body. She is betrayed, but likewise feels great pity for the girl. As she is there, a weasel enters and is struck dead by one of her servants. Soon after, another weasel enters to find its partner dead, and then escapes the servant's attacks. The second weasel soon returns with an herb from the forest, and uses it to bring the first back to life. Guildeluec has the servant fetch the herb from the weasels, and she uses it to wake Guilliadun. The latter wakes and tells Guildeluec her story of betrayal, believing herself to have been abandoned by Eliduc, ending with "She who trusts a man is extremely foolish." Guildeluec calms her down, speaks to the truth of her husband's grief, and promises she will soon take the veil (become a nun), which will leave them free to marry.
Guildeluec sends a servant to fetch Eludic, who quickly joins them, kisses his maiden and thanks his wife "gently." Guildeluec sees their love and asks Eliduc's permission to separate from him and take the veil, perhaps founding an abbey on his land. He grants this, and she establishes a proud order.
Eliduc and Guilliadun marry, and have a great love. They both are "turned to God" and Eliduc ultimately builds a great church to which he devotes most of his land and wealth. He joins his own order while his wife joins his first wife and each of them "came to a good end thanks to God, the true divine."
Like in the case of "Guigemar," the first lay in this collection, this final lay earns its special placement by emphasizing all of the recurring themes of the lays. And yet this lay, the longest by far of all twelve, is unique in its particular contradictions and complexities.
Consider the titular character, Eliduc. It is much more difficult to determine whether Marie means us to criticize or praise Eliduc than it usually is with her protagonists, mainly because he seems to illustrate both selfless love and self-involved love. His understanding of loyalty is without question – he serves both lords well, he has a happy marriage before leaving Brittany, and he continues to remember his obligation to Guildeluec throughout his mental turmoil. Unlike Equitan, who understood the demands of loyalty but was able to easily delude himself through faulty reasoning, Eliduc never fully absolves himself of his duty towards Guildeluec.
Partly, this is due to his understanding of moderation. Marie gives us an explicit instance of his moderation when he only takes a "moderate amount" of wealth form the lord of Tontes, and also in the way he stresses that his men should not accept gifts too quickly or willingly from their hosts at Tontes. Likewise, Eliduc is able to abstain from consummating his relationship with Guilliadun, and in fact never even kisses her until she swoons and he is overcome by concern for her. In all these ways, Eliduc shows a devotion to selfless love.
And yet Marie paints him in such a way that we cannot help but recognize his selfishness. It is true that he remembers his wife throughout his time in Tontes, and yet in a sense he merely honors the letter of the law rather than its spirit. While he does not sleep with Guilliadun, he certainly does allow himself to get emotionally involved, in the process allowing her to be led on and creating a situation where he will either have to take her to Brittany or leave her to suicide. He is well aware of her affection – she sighs tellingly in their first meeting – and yet continues to facilitate meetings between them. The knight most admired for his prowess on the battlefield is perhaps too accustomed to affection not to let himself revel in it when it's available. There are more clues that Eliduc is not as perfect as he'd like to believe. For one, his victory for the lord of Tontes is decisive, but hardly heroic in the way he ambushes his enemy. Further, he allows his self-pity and sadness to pollute his relationship with Guildeluec when he first returns to Brittany, in effect refusing to allow his old life to return so that he can feel justified in leaving her again for his new love. And lastly, the way he throws the sailor overboard – the sailor who tells the truth! – mirrors his own king's lack of loyalty to him at the start of the lay. In the same way the King of Brittany believes unjust slander and banishes Eliduc, so does Eliduc kill his own subservient sailor in a lapse of loyalty based solely on an emotional reaction, something the sailor does not deserve.
Fate and magic both play a role in this lay, mainly in the way that love is again painted as something outside of human control. Eliduc cannot be faulted for falling in love with Guilliadun, but he can be faulted for the way he responds to these forces. As noted above, he continues to indulge his desires even as he is passive about admitting the existence of his wife. He wants to have his cake and eat it too, and for this he deserves our disapproval. Contrast this with the behavior of Guildeluec, who realizes she has in her power a magic herb to revive the young maiden, and does not hesitate to do so, even if it spells a necessary unhappiness for her. This level of selflessness is unknown to Eliduc, which suggests not only that he chose poorly for his carnal love and that he does not deserve the superior woman, but also that the superior woman (Guildeluec) realizes this to be true and thus sets him free.
Marie's ultimate point is, as always, that purity of love cannot exist in the public world. The world of "Eliduc" is not full of people who behave attractively – the king of Brittany unfairly condemns his vassal as did Arthur to Lanval, the old king in Tontes is overly protective of his daughter as are fathers in several other lays, and even the pure Guilliadun resorts to trickery to resolve her uncertainty about Eliduc's love – and yet love persists. Marie suggests in the end of the lay that the only way to find serenity through love in this world is by making oneself subservient to the charity of selfless love, epitomized in God. The end of the lay finds the superior Guildeluec opening the door to a life of devotion before the lord, a door through which both Eliduc and Guilliadun follow her. By the end, they all adore their beloved from afar and through correspondence, praying for rather than touching each other, and are happy in this. It is the final word of Marie's insistence that the world destroys love: a lover can still find happiness if he or she recognizes love itself is due to the charity of the Lord, and so might we be willing to recognize ourselves as inferior to such pure selflessness.