Set in the fantasy world of Alagaësia more than a year after the events of the
Inheritance Cycle, this standalone novel follows Murtagh, a Dragon Rider bonded to the red dragon Thorn, as he investigates a sinister cult while struggling with guilt and isolation. Murtagh's father, Morzan, was one of the Forsworn, the thirteen Dragon Riders who betrayed their order to serve the tyrant King Galbatorix. During the war, Galbatorix used magical oaths in the ancient language, the tongue that governs all magic, to enslave Murtagh and Thorn, forcing them to commit atrocities including torturing Queen Nasuada, the realm's current ruler. Although they helped bring about Galbatorix's defeat, the world regards them as traitors, and they live as self-imposed exiles in the wilderness.
Murtagh enters the northern city of Ceunon under an alias to meet Sarros, a trader he has been paying for information about strange, brimstone-scented places at the edges of the land. At an inn, he befriends Essie, the innkeeper's young daughter, whose burn scar stirs memories of his own childhood wound. Sarros arrives with a sulfurous, glowing stone but betrays Murtagh and holds Essie hostage, revealing that a witch-woman named Bachel enchanted protective bird-skull amulets for his men. Murtagh uses the Name of Names, the secret true name of the ancient language known only to him, his half brother Eragon, and the elven queen Arya, to strip the wards and defeat the attackers. Sarros dies raving about "the Dreamers" who twist people's thoughts. Before fleeing, Murtagh heals Essie's scar with magic.
Murtagh and Thorn fly to Gil'ead seeking intelligence. Carabel, a werecat—one of Alagaësia's secretive shapeshifting beings capable of taking both human and cat form—intercepts his inquiries and proposes a bargain: She will share what she knows about Bachel if Murtagh rescues her kidnapped daughter Silna, a werecat kitten imprisoned beneath the city guard's barracks. Under a false name, Murtagh kills Muckmaw, a magically enhanced giant sturgeon terrorizing a nearby lake, and joins the guard. That night, he explores catacombs beneath the barracks, discovering hidden chambers, a Ra'zac egg (Ra'zac being insectoid predators that feed on humans), and the cell where Silna was held. He takes a compendium of the ancient language and a yellow diamond charged with energy. Fighting his way out, he finds a bird-skull amulet on a magician from Nasuada's guild of spellcasters, proving the Dreamers have infiltrated the queen's forces. Silna reaches Carabel on her own, and the werecat reveals that Bachel leads a cult called the Draumar ("The Old Dreamers") in a sulfurous village along the Spine mountains. Murtagh writes to Nasuada warning her of the infiltration.
As Murtagh leaves the fortress, Lyreth, a nobleman and childhood bully from Galbatorix's court, ambushes him and tries to recruit him for a conspiracy to restore the Empire. Murtagh refuses, and Lyreth traps him in a device designed to suffocate magicians. Thorn crashes through the building to save Murtagh, but the dragon's childhood trauma of being confined by Galbatorix triggers a panic, and Thorn rains fire on Gil'ead. The destruction eliminates any chance of Murtagh publicly clearing his name. During the journey north, they visit Ristvak'baen, the ruined tower where Galbatorix killed the Rider leader Vrael, and practice entering enclosed spaces to address Thorn's claustrophobia.
They locate Nal Gorgoth, a sulfurous valley of ancient stone buildings. Bachel, a striking, ageless woman of half-elven heritage who claims the title of Speaker, the chosen voice of a being she calls the Dreamer of Dreams, welcomes them. She declares their arrival prophesied, calling them "the saviors of the world," but insists they first experience the valley's dreams. That night, Murtagh and Thorn share vivid nightmares of a black sun and a wingless dragon of apocalyptic size. Exploring secretly, Murtagh discovers a cavern behind the temple with a bloodstained altar and evidence that Forsworn members visited Nal Gorgoth. When Murtagh presses Bachel for answers, she causes a devastating earthquake, demonstrating power beyond any known magician. He resolves to explore the cavern and escape.
In the caves, Murtagh finds the Well of Dreams, a shaft emitting sulfurous vapor. Bachel and her lieutenant Grieve confront him. The witch wields Niernen, a Dauthdaert, one of twelve elven-forged lances designed to kill dragons. She releases a choking cloud of the Breath, a vapor tied to Azlagûr the Devourer, the being the cult worships. Murtagh inhales the vapor and falls under her power. Both he and Thorn are imprisoned, with Murtagh force-fed vorgethan, a drug that prevents spellcasting. In the neighboring cell, he finds Uvek, a shaman of the Urgals, a horned humanoid warrior race.
Bachel tortures Murtagh with sharpened onyx claws and mental assault, trying to force his fealty to Azlagûr, whose sleeping mind she claims generates the dreams that shape reality. She reveals she personally turned young Galbatorix against the Riders after his dragon Jarnunvösk died and that Morzan trained in Nal Gorgoth. Murtagh resists by drawing on lessons from past ordeals and reflecting on Nasuada's endurance under similar conditions. Eventually, the Breath, vorgethan, and relentless pressure break his active will. He and Thorn become compliant thralls, retaining only a buried ember of self-awareness.
Under Bachel's control, Murtagh slaughters a group of fleeing tribespeople including women and children. The horror cracks through his compliance. Alín, a white-robed temple acolyte troubled by Bachel's cruelty, begins secretly bringing Murtagh food free of vorgethan. As the drug clears, Uvek proposes the rite of
qazhqargla, an Urgal blood-brotherhood ceremony, and they become sworn brothers. When the festival of Black Smoke, a major Draumar observance, arrives, Bachel prepares to sacrifice prisoners and places the dagger in Murtagh's hand. Drawing on the combined strength of Thorn and Uvek, Murtagh channels energy from the hidden yellow diamond into Uvek's healing charm, breaking the Breath's hold. He refuses the command and frees Thorn.
Murtagh fights through the temple while Thorn destroys the village above. He kills Lyreth, who is among the noble guests at the festival, and retrieves Zar'roc, his red-bladed sword, from a chest behind the dais. Fighting alongside Uvek, he ignites Zar'roc in crimson flames and cleaves Grieve's skull. Murtagh descends alone into the caverns, using the Name of Names to rename his sword from Zar'roc (Misery) to Ithring (Freedom). Deep underground, he reaches Oth Orum, a vast crystal-lit chamber where Bachel waits in dragon-scale armor, wielding Niernen, with acolytes holding Alín captive. Alín breaks free and shields Murtagh with a bird-skull amulet. Despite being stabbed through the lung by Niernen, Murtagh collapses a crystal pillar onto Bachel, then kills the Speaker with Ithring.
Before losing consciousness, Murtagh senses a mind of impossible size stirring in the void beneath the chamber: cold, ancient, and filled with malevolence. He directs all remaining light into the void, triggering an explosion that begins collapsing the mountain. Thorn conquers his lifelong claustrophobia to enter the cave and rescue Murtagh, with Uvek riding on the dragon's back and applying the healing charm.
Murtagh wakes four days later in Ilirea, the renamed former capital, healed by Nasuada's spellcasters. Both he and Thorn speak their changed true names, reflecting their growth. Nasuada visits, and Murtagh recounts everything, including the massacre and his breaking under torture. He warns her of the Draumar's infiltration and reveals that a familiar but unplaceable figure at Bachel's gathering may be a traitor in her court. Nasuada appoints Alín as a royal maid, keeping a valuable intelligence source close, and asks Murtagh to stay, not as a prisoner but as a trusted ally. After they acknowledge their feelings for each other, Murtagh agrees, choosing connection over exile for the first time in his life.