The tale begins with the dragon-slayer Sigurd, son of Sigmund, who journeyed across the world after the death of the great serpent Fafnir. Sigurd was a man of unparalleled strength and beauty, possessing the wisdom of the birds and the wealth of the Glittering Heath. On his travels, he came upon Hindarfjall, a mountain peak wreathed in a flickering wall of magical fire. Without fear, Sigurd spurred his horse, Grani, through the flames and discovered a figure clad in armor, trapped in an enchanted sleep. When he cut away the mail-coat, he revealed the Valkyrie Brynhild. She had been punished by Odin for her disobedience and placed in this slumber, decreed to marry only the man who knew no fear. Sigurd and Brynhild exchanged vows of love and rings of gold, specifically the ring Andvaranaut, which carried with it both a great fortune and a heavy curse.
Sigurd eventually departed, promising to return and claim her as his bride. However, his journey led him to the hall of the Gjukungs, the Burgundian royalty. There, the queen-mother Grimhild, a woman of great magical skill and ambition, saw in Sigurd a perfect match for her daughter Gudrun. Fearing that Sigurd’s heart was already tethered elsewhere, Grimhild prepared a potion of forgetfulness. When Sigurd drank the draught, the memory of Brynhild, the mountain of fire, and his sacred oaths dissolved like mist in the morning sun. He looked upon Gudrun with new eyes, fell in love, and married her, becoming a blood-brother to her brothers, Gunnar and Hogni. The treasure of the Volsungs and the fame of the dragon-slayer were now tied to the house of the Gjukungs, just as Grimhild had intended.
Months later, King Gunnar sought a wife of his own, and his mother suggested the famous Brynhild. Gunnar, Sigurd, and Hogni rode to her hall, but the ring of fire still blazed, and Gunnar's horse refused to cross the threshold. Even when Gunnar mounted Sigurd's horse, Grani, the beast would not move for a man who lacked the true spirit of the predestined hero. Knowing only one way to help his brother-in-law, and still under the influence of the potion, Sigurd used the magic taught to him by Grimhild to exchange shapes with Gunnar. In the guise of Gunnar, Sigurd rode through the flames. Brynhild, bound by her oath to marry the man who crossed the fire, accepted him, though her heart was heavy with confusion. For three nights they shared a bed, but Sigurd placed his sword, Gram, between them, remaining faithful to Gudrun while acting as Gunnar's proxy. Before leaving, he took the ring Andvaranaut from her finger and gave it to Gudrun later as a trophy, replacing it with another.
Brynhild married Gunnar, but the air in the Burgundian hall was thick with unspoken tension. The deception might have remained hidden forever had it not been for the vanity of the two queens. One day, while washing their hair in the river, Brynhild waded further upstream, claiming that her husband was more courageous and that she should not be touched by the water that had washed Gudrun’s hair. She boasted that Gunnar had ridden through the fire while Sigurd was merely a servant of the king. Gudrun, stung by the insult, revealed the devastating truth: it was Sigurd who had braved the flames, and it was Sigurd who had taken the ring from Brynhild’s hand. She held up the ring Andvaranaut as proof of the trickery. The world shattered for Brynhild in that moment. She realized she had been cheated out of her true husband and forced into the arms of a man who was not her equal.
Brynhild retreated to her chambers, falling into a deep and dark melancholy. She refused to eat, speak, or move, her mind a cauldron of shame and fury. When Gunnar finally forced his way into her room to comfort her, she met him with vitriol. She told him that she had been betrayed and that her life was a mockery. Her love for Sigurd had turned into a poisonous jealousy; she could not bear the thought of him living with Gudrun, knowing that they shared the life she was meant to have. She gave Gunnar an ultimatum: either he must kill Sigurd to avenge the slight to her honor, or she would leave him and take her dowry with her, plunging his kingdom into ruin. Gunnar was torn. Sigurd was his blood-brother, and they had sworn oaths of protection, but the pressure of Brynhild's rage and the fear of losing his status drove him to a dark decision.
Gunnar and Hogni consulted together. Because they had sworn oaths of brotherhood to Sigurd, they could not spill his blood themselves without inviting the wrath of the gods. Instead, they manipulated their younger brother, Guthorm, who had not sworn the oath. They fed Guthorm a mixture of wolf's flesh and snake's venom to incite a murderous frenzy in his heart. While Sigurd lay asleep in his bed beside Gudrun, Guthorm crept into the room. Twice he hesitated, seeing the golden light of the hero’s eyes even in sleep, but on the third attempt, he drove his sword through Sigurd’s body. With his dying strength, Sigurd flung his sword, Gram, at the fleeing Guthorm, cutting him in two. Sigurd breathed his last in Gudrun’s arms, whispering of the treachery that had brought him down.