Calamity by Brandon Sanderson

David Charleston has changed. No longer the vengeance-driven teen who wanted to kill Steelheart, David is now the leader of the Reckoners—and one of the few people who still believes there’s hope for the world and for the Epics themselves.

But that hope is tested like never before. After the shocking fallout of Firefight, the Reckoners are in disarray. Prof, once their leader and mentor, has succumbed to the corruption of his Epic powers and become one of the very tyrants they used to fight against.

Now, David and his small, determined team must confront Prof and try to bring him back—while also discovering the truth behind Calamity, the mysterious red star in the sky that gave the Epics their powers. What is Calamity, and why does it seem to influence the Epics toward destruction?

The answers could mean salvation... or the end of everything.