Mistborn #03 The Hero of Ages

Ferson Penrod as their king instead of Elend. Oddly, however, being deposed finally made Elend begin to understand what it meant to be a king and leader. He began to intertwine his philosophies about justice with the things Tindwyl was teaching him, and actually started to become an inspiring and effective leader—even if he no longer held the throne. The city's problems, however, grew even worse as Jastes Lekal's koloss arrived. It quickly became clear that he had only marginal control over the murderous beasts.
    Eventually, Zane prompted Vin to assault Cett's base inside of Luthadel. (Cett had entered to make a play for the throne himself.) She and Zane slaughtered their way to the top floor of the keep, where Vin had a breakdown prompted by what she'd just done. She fled, leaving Cett alive. Soon after, Zane attacked her, driven to madness by strange voices in his head. Vin and Zane fought, and OreSeur revealed himself as a spy, another kandra named TenSoon, who had killed and impersonated the real OreSeur. Vin managed to kill Zane, even though he had atium, then she ran to Elend. Her emotional problems in remission, she convinced Sazed to marry Elend and her.
    Following his near-assassination, Cett retreated from Luthadel and withdrew his armies from the siege. Elend's attempts to get Jastes to withdraw were unsuccessful. Outside, Straff realized that if he simply pulled back, the koloss would probably attack and destroy the city—leaving Straff himself to return and take control once the beasts had exhausted themselves in combat.
    Many of the crewmembers realized that this was what would happen. Sazed convinced them that they should lie to Vin and Elend, telling them that the city would be safe and sending them north to search for the Well of Ascension. This ploy succeeded. Vin and Elend left, taking Spook with them, and in their absence the koloss finally attacked. The city's army fought well, Sazed himself holding one of the city gates against terrible odds. During the fighting, Clubs, Dockson, and Tindwyl were killed. As the koloss were about to destroy everything, Vin returned to the city, having learned from Spook that she had been deceived.
    Vin exploited an Allomantic weakness in the koloss revealed to her by TenSoon/OreSeur the kandra, taking control of the koloss in the same way the Lord Ruler once had. She used those koloss to attack Straff's army when it returned, and she was joined by Cett at the last moment. With Straff dead, Vin forced Penrod, Cett, and Straff's second-in-command to swear allegiance to Elend, naming him emperor.
    The city was saved. However, Vin continued to hear the strange thumpings in her mind. She'd become convinced that she—not the ancient man Alendi—was the Hero of Ages. She soon realized that the Well of Ascension wasn't actually in the northern mountains, but instead beneath Luthadel. She and Elend investigated this, discovering that beneath Kredik Shaw, there was a large secret cavern stockpiled with food. Beyond that cavern was another, filled with dark smoke. Beyond that, a pool of glowing power. The Well of Ascension.
    Sazed, up above, was still reeling from Tindwyl's death. He had thrown himself into his studies, and discovered—to his alarm—that something was very wrong with the prophecies. He rushed after Vin and Elend, intent on stopping them from taking the power at the Well, but was blocked by Marsh. As the two fought, Vin took the power and did what she thought was the right thing. Though the mist spirit stabbed Elend, Vin didn't use the Well's power to heal him. Instead, she released it as the prophecies said she had to do in order to stop the mists from destroying the world.
    She made the wrong choice. A dark force imprisoned near the Well of Ascension had altered the prophecies and led Vin to do what was necessary to release it. The thing burst free, leaving Vin with the horror of what she had done. The mist spirit, however, provided a way for her to save Elend by making him into a Mist-born.
    The book ended with Vin and Elend on the walls of Luthadel, having saved the city but also having released a terrible force upon the world. Sazed, crushed by Tindwyl's death, had come to believe that his faith was worthless. Spook was riddled with guilt for abandoning Clubs to die in the city, and both Breeze and Ham bore emotional scars from their seemingly hopeless fight against the koloss. On top of all this, as Sazed had reported, the mists had changed