Plot
The Final Empire is in turmoil as various regions descend into anarchy following the Lord Ruler's death and the disappearance of the Steel Ministry. Elend Venture has claimed the crown of the capital city, Luthadel, and attempts to restore order, but various hostile forces converge on the city. Three armies lay siege to Luthadel because of its rumored wealth of Atium and political influence. The first army is led by Straff Venture - head of House Venture, and Elend's father. The second army is led by Ashweather Cett, self-declared king of the Western Dominance. The third army consists of Koloss, massive, brutish blue creatures once controlled by the Lord Ruler, and is led by Elend's former friend Jastes, who is buying the Koloss' obedience with counterfeit coins.
Vin and Elend discover a set of discarded bones in their keep, and with help from Vin's shapeshifting Kandra, OreSeur, realize that another Kandra has taken the form and identity of one of Kelsier's crew to spy on them. Vin becomes increasingly suspicious of everyone around her. At night, she begins sparring with Zane, Straff's Mistborn son and Elend's half brother. In the South, Sazed has come across suspicious deaths that appear to be caused by the mists. Marsh – Kelsier's brother and a Steel Inquisitor – leads Sazed to a Ministry stronghold called "The Conventical of Seran," the former base of the Inquisitors. They discover an engraving that was authored by the Terrisman who once claimed to have found the Hero of Ages, which begins "I write these words in steel, for anything not set in metal cannot be trusted." They leave quickly, Sazed taking a charcoal rubbing. On their way back to Luthadel, Marsh disappears.
The Terris keeper Tindwyl arrives at Luthadel to train Elend to be a better king. Despite his personal improvements, the Assembly votes to depose Elend, using the very laws written by Elend, and elect Lord Penrod as their new king. Zane pressures Vin to kill her enemies and flee with him, abandoning the city. Misting assassins attack Elend at an Assembly meeting, and when Vin brutally kills them in front of Elend, their relationship deteriorates. At Zane's urging, Vin lashes out, slaughtering hundreds of Cett's soldiers at his temporary Luthadel mansion. She becomes disturbed by her actions and flees without killing Cett, who decides to leave the city and abandon his siege. Vin decides to choose Elend over Zane and refuses him. He tries to kill her, and reveals that the real OreSeur is dead, having been replaced by Zane's kandra, TenSoon. TenSoon has grown to like Vin, however, and he helps her kill Zane before returning to the kandra homeland. Feeling liberated, Vin accepts Elend's longstanding marriage proposal. Sazed and the rest of the crew scheme to get Elend and Vin out of the city before it falls, and Sazed creates a false map to the Well of Ascension, which Vin is convinced may be able to save them.
Sazed and Tindwyl have been studying the mysterious text left by the Terrisman Kwaan, which explains the events of the Lord Ruler's ascent. Kwaan had believed he had discovered the Hero of Ages in the person of Alendi, who rose to become a feared general and ruler known as the "Conqueror". However, Kwaan had become fearful for an obscure reason, believing that Alendi was not actually the Hero of Ages and became afraid of what would happen when he reached the Well of Ascension and tried to use the power within. To prevent this, Kwaan had instructed his nephew Rashek to mislead Alendi or kill him if he needed to. Rashek obeyed his uncle's command, but instead claimed the power for himself and became the Lord Ruler. Sazed and Tindwyl's research is complicated by their disagreements over the nature of the Hero of Ages prophecy, and Sazed becomes convinced that Vin herself is actually the Hero of Ages. At some point, one fragment of the text Sazed has transcribed from his metalminds is mysteriously ripped off.
Straff withdraws his forces, allowing the koloss army to attack Luthadel, planning to rescue the city after the koloss have destroyed most of it and suffered casualties. Jastes loses control of his army; he flees and is killed by Elend. Vin returns to Luthadel just in time to save Sazed and most of the city's civilians, though Dockson, Tindwyl, and Clubs are killed. She discovers that she can control the koloss using her Allomancy; she stops their slaughtering and turns them and Luthadel's army against Straff's army. Vin kills Straff and his generals as Cett decides to ally himself with Luthadel. Vin forces Cett, Penrod, and Straff's last general to swear allegiance as kings under Elend, whom she names emperor.
Vin realizes that the Well of Ascension is in Luthadel itself; Rashek had transferred it from Terris to his stronghold when he had remade the world after claiming the Well's power, ensuring that he could keep it close and hide it from others. Vin, Elend and Spook find a hidden doorway in the Lord Ruler's castle that leads down to the underground Well of Ascension, where a man made of mist stabs Elend. Meanwhile, a similar spirit approaches Sazed, revealing the fragment of text which had disappeared from his and Tindwyl's transcription: Alendi must not reach the Well of Ascension, for he must not be allowed to release the thing that is imprisoned there. Sazed attempts to stop Vin but is attacked by Marsh, who appears to struggle with his quest to kill Sazed. Sazed is saved by Ham, and Marsh escapes. Meanwhile, Vin is tempted to use the power in the Well to heal Elend, but ultimately follows the instruction of Sazed's rubbing, releasing the power for the good of the world rather than seizing it for herself. The moment she releases it, a powerful entity escapes, shouting out that it is now free. The Mist figure encourages Vin to feed Elend a bead of metal she finds in the room, which makes him a Mistborn; his life is saved through Allomancy by burning Pewter.
Two months later, Sazed returns to The Conventical of Seran and inspects the engraving. He discovers that the words of the rubbing have been changed, finally explaining why Kwaan had inscribed it in metal where it could not be altered. Even the text in Sazed's metalminds had been manipulated, presumably by the mysterious entity working to secure its own release. Realizing that he had been manipulated and the entire Hero of Ages prophecy had been a lie designed to release the power hidden in the Well of Ascension, Sazed loses his faith.
