The arena nearly kills Arn, but Vasilia's coin gives him a second life. He wakes on a physician's slab, discovers the gleaming armband he cannot remove, and meets Ignius, the faded lanista who needs victories. Ignius tells him to fight, win the solstice games, and maybe find a healer for his tongue; refuse, and the Imperial administration will chain him to a galley. Arn understands the game immediately. The contract is just ink, and he plans to break it, but first he has to regain enough magic to survive. He trains with Mahan, takes abuse from the convict Marcus, and knocks Marcus flat with one fist to establish his place. The weapons master gives him a wooden sword only when Arn proves he can fight. Every day without magic feels like blindness, and the only cure is a body dying on the sand. The hook is simple: Arn needs a kill, and Mahan will not let him into the arena until he is ready.

Arn finally gets his first arena fight, kills the opposing gladiator without waiting for mercy, and feels the man's life force flow into him. The stolen energy makes the seed sprout, but it also leaves him retching and weak. He uses a fake prayer to get permission to leave the ludus, finds the Tyrian quarter, and meets Helgi the loremaster. Helgi cannot repair the ruined runes on Arn's scarred skin, but he can create rune tokens. The price is set by a criminal named Magnus, and Arn becomes a hitman. His first job is murdering three men in a slum house; they turn out to be runaway serfs, and a boy sees his face. Worse, the last man Arn leeches life from rises later as a shambling undead. Domitian tells Arn about the monster in the streets, and Arn realizes his shortcut has a cost. A spellbreaker named Atreus is already asking questions, and the trail leads straight toward him.

Arn restores his runes of force, subtlety, swiftness, and recovery through Helgi's tokens while working for Magnus and then Aja. He kills Vera, kills Karl, outmaneuvers Magnus's betrayal, and takes over the criminal arrangement. In the solstice games, he faces Cassian, the previous champion, and discovers Cassian also wields magic. Arn kills him anyway and becomes champion. The victory feast is at the mansion of Salvius, the mageknight who ambushed Arn, cut out his tongue, and threw him to the lions. On Salvius's wall hangs Arn's own rune sword and the eagle feather from his tribe. Salvius does not recognize him, but Arn later scales the wall, wakes his enemy, and hands him a written duel challenge. He kills Salvius with the stolen sword and carves the blood eagle into his back. Then he crashes into Helena's convent, kills Sister Joanna who abuses the nun, and hides until Atreus finds his sword under Iris's bed and captures him.

Atreus interrogates Arn and leaves for Archen. In the dungeon, Helena visits, removes her veil, and kisses him; a soft glow heals him, restoring even his tongue. Then Vasilia has Arn dragged to the Arcane Tower, takes back the tracking armband, and reveals that she planned his recovery all along, so she can sacrifice a fully charged vessel at the celestial conjunction. Arn pretends to swallow the sleeping draught, uses a hidden needle to stay awake, headbutts her, and speaks his first words: "You'd be surprised." He kills her by using a rune of attraction to pull the broken gate into her back, impaling her on his sword. He escapes, frees the gladiators, releases the arena lions, and tears the arena apart with an earthquake. At the harbour, the fugitives steal a warship, Helgi breaks the chain with earth magic, and as the tower's ritual fails in distant Archen, the uncontrolled explosion ripples through Aquila and destroys the city. The shockwave pushes the ship out to sea, and Arn, who fell short of the deck, is dragged aboard by Sigismund.