It has been a year since Vin, the Mistborn skaa, killed the Lord Ruler. While Kelsier, Vin’s mentor and the mastermind behind the plot to take over the Final Empire, had hoped the tyrant’s death would mean a better world for all, the world is still in turmoil.
Because of the Lord Ruler’s death and the disappearance of the Steel Ministry, the Final Empire’s religious and the ruling government body, various regions have fallen into anarchy. With the help of Kelsier’s old crew, Elend Venture has claimed the crown and attempted to stabilize the capital city of Luthadel by forming a parliament-like assembly made up equally of working skaa, skaa merchants and noblemen.
Unfortunately, three armies lay siege outside the city’s wall. Rumors of the Lord Ruler’s Atium horde and the political importance of Luthadel have attracted Straff Venture, Elend’s father, with the largest army in the north; Ashweather Cett from the west; and an army of koloss under the control of Elend’s former friend, Jastes. (Koloss are blue, humanoid creatures whose bodies keep growing until their hearts can no longer support their massive size.) As each army waits to see what the others will do, Luthadel runs low on food and resources and high on fear.
While Elend is skilled in theories of leadership, he lacks experience. His rule becomes unstable as members of Luthadel’s assembly vie for power. At Sazed’s request, a Terriswoman named Tindwyl arrives in Luthadel to help teach Elend to be a more authoritative king. Tindwyl’s teachings pay off, and Elend convinces the crew that he should meet with both Straff and Cett, manipulating the other kings to attack each other.
Straff intends to kill Elend after their meeting, but after feeling Vin’s powerful Allomantic control of his emotions, he is afraid and allows Elend to live. For the first time in his life, Elend is taken seriously, but it’s too late. While Elend meets with Straff, the assembly deposes him.
As Elend works to get the assembly to reinstate him, Vin is experiencing her own turmoil over her self-worth. A year before, she turned down Elend’s marriage proposal. Despite loving him, she doesn’t think she is good enough for him.
Complicating her feelings is Zane, Straff’s illegitimate Mistborn son and Elend’s half-brother. He spends his evenings sparring in the mists with Vin, seducing her and driving a wedge between her and Elend. Vin has also become suspicious of the mists, noticing they come earlier in the evening and stay later into the morning. She senses an ominous spirit in the mists and fears it will attack her. She feels Allomantic pulses that she believes are coming from the Well of Ascension, the mythical source from which the Lord Ruler got his power.
Vin also has another problem. A kandra, a being who takes the bones and form of another, has taken the form and identity of one of Kelsier’s crew to spy on their hidden strategies. Vin enlists the help of her own kandra, OreSeur, now in the form of a large wolfhound, to help her root out the spy.
Sazed, who has been tasked by the Terris Synod to teach the skaa in the south of the Final Empire, is tracked down by Marsh, Kelsier’s brother and an Inquisitor. Marsh asks Sazed to go with him to a Steel Ministry compound, The Conventical of Seran, where the Inquisitors and Obligators of the Lord Ruler’s religion fled after the collapse. There, they find that the Inquisitors and Obligators murdered all their servants. They also find an inscription etched in a large steel plate written by the Terrisman Kwann, the one who discovered Alendi, the man believed to be the Hero of Ages. Rashek, the Lord Ruler, killed Alendi to take the power at the Well of Ascension.
Sazed abandons his teaching and returns to Luthadel to translate the inscription and do research, as he, too, is concerned about the mists, having heard reports that the mists have been attacking and killing people in the daytime. While Tindwyl helps Sazed with his research, she disapproves of his rebellious nature and his role in defeating the Lord Ruler, yet she admires his bravery and is in love him. Sazed feels just as strongly for Tindwyl, but doesn’t feel worthy of her because he is a eunuch.
Straff’s assassins attack Elend at an assembly meeting, and Vin kills them, making this the first time Elend has seen her work as a Mistborn. The look of horror on Elend’s face causes their relationship to deteriorate further. The looming armies and constant fear of assassins cause Vin to feel a loss of control, making it easy for Zane to convince Vin that Cett sent the assassins.
The two Mistborns attack Cett and kill hundreds of his men. Vin, convinced that Cett is Mistborn, confronts the man, but when she realizes he is not, she leaves him alive and goes into hiding. With OreSeur’s help, Elend finds Vin and tells her that while he doesn’t understand why she attacked Cett, he trusts and supports her decisions. After the loss of his soldiers, Cett decides to abandon his siege and leave Luthadel.
Zane tells Vin that Elend will never understand her like he does and finally convinces her to leave Luthadel with him. Remembering Elend’s words of trust, Vin changes her mind, telling Zane that she will stay and support Elend. Zane is enraged and tries to kill Vin, telling her that his kandra TenSoon killed OreSeur and has been the spy impersonating her kandra. TenSoon, who has grown fond of Vin but is being forced to work for Zane, warns Zane that Vin knows of the kandra’s weakness to Allomancy. Vin uses the hint to control TenSoon, forcing him to help her, and she kills Zane.
Finally, sure of what she wants, Vin accepts Elend’s proposal, and Sazed marries the two. Sazed, fearing that they will all be killed when one of the remaining armies takes the city, conspires with the rest of the crew to get Vin and Elend out of Luthadel. He draws a fake map to the Well of Ascension because Vin feels compelled to go there.
With Cett’s forces withdrawing, Straff strategically withdraws his own forces, encouraging the koloss army to attack Luthadel. Straff plans to let the koloss weaken Luthadel before coming in as the hero to rescue the city. Vin learns of Sazed and the crew’s deception and returns to Luthadel just in time save Sazed from being killed.
She realizes that the same Allomancy used to control the kandra works on the koloss, and she manages to stop the widespread slaughter and destruction, but not before Tindwyl and some crewmembers die. Vin uses the newly controlled koloss, and with rest of Luthadel’s army, she attacks and kills Straff and his generals. Cett returns and allies with Luthadel against Straff’s armies. After the victory, Vin tells the armies that Elend is the new emperor of the Final Empire.
The city is saved, but Vin still hears the Allomantic pulses in her mind. Convinced that she is the legendary Hero of Ages, Vin realizes the Well of Ascension has been in Luthadel the entire time. She finds a secret doorway in the Lord Ruler’s castle that leads down to underground caves.
Sazed, stricken with grief over Tindwyl’s death, goes over the research and translations they did together. The writings all say the power at the Well of Ascension must be released, but there are inconsistences in the information he has gathered. As he tries to figure them out, the mist spirit that has been following Vin appears to him and directs him to stop Vin and Elend. It leads Sazed to the Lord Ruler’s castle.
Once there, he is surprised when Marsh confronts him, and the two fight. Marsh tells Sazed he is not acting of his own free will, but he must kill him. They fight and Sazed survives with the crew’s help, but it’s too late to stop Vin.
Vin and Elend find the Well of Ascension, but the mist spirit appears and stabs Elend. Vin knows that if she takes the power in the well, she can heal Elend and even more, fix all the problems in the world. She also fears that the power will corrupt her, as it did Rashek 1,000 years before. Vin goes into the well and decides to release the power to save the world instead. As soon as she does, the entity trapped within the well bursts free. Vin is horrified at the mistake she made, but it’s too late.
The mist spirit appears again and urges Vin to feed Elend a small piece of unknown metal. After he swallows it, he becomes Mistborn and starts to heal himself with Allomancy. Vin understands that the mist spirit stabbed Elend to get her to take the power of the well and heal him. It did not want her to release the entity trapped in the well. Elend recovers, but he and Vin are concerned as they don’t know what the future holds. The mists are killing and making people sick more than ever.
Sazed travels back to The Conventical of Seran. Upon re-examining the inscription, Sazed sees that it is different from what he recorded. The writing says that the entity that is trapped in the well is crafty and able to change anything not written in metal. Most importantly, it must never be released from the Well of Ascension.