Twelve years ago, an object dubbed Calamity appeared near Earth and burst in the sky, emitting a strange radiation which gave a small group of humans super powers and near invincibility in apparent defiance of the known laws of physics. They all have different types of powers and weaknesses, with no apparent rhyme or reason. Dubbed Epics, these super-humans took to crime. Existing government proved absolutely incapable of controlling the Epics, the most powerful of which replaced government authority and enslaved the rest of humanity.
Ten years ago, an eight-year-old Chicago native boy named David Charleston was orphaned when the High Epic Steelheart murdered his father while fighting a rival Epic, Deathpoint in a bank. The sole survivor of the bank carnage, David has now come of age in what is known as Newcago, ruled by Steelheart. David witnessed Steelheart's one weakness as his father inflicted a minor wound at Steelheart's eye while trying to shoot the other Epic, and David has grown up devoting his life to learning all he can about the Epics to find their weaknesses, with the goal of avenging his father. He finds "the Reckoners", an elite group led by "Professor" Jonathan Phaedrus with the common goal of killing as many Epics as possible. They decide to admit him into their group when they discover he has witnessed Steelheart's weakness, and his collected research.
Steelheart has turned most all of Newcago into steel with his power, and his lieutenant Nightwielder keeps it in eternal darkness by hiding the Sun. The mortal citizenry live mostly underground and work at menial factory jobs. Yet Steelheart has proved one of the more effective Epic rulers, by providing Newcago with infrastructure (food, water, and electricity) in contrast with most other cities in what is now known as the "Fractured States".