Thousands of years after the death of Percy Jackson and his friends, western civilization is coming to an end. The gods are weak, and many have faded away. A new, more powerful race of demigods has risen, and they are being used by Kronos. They have overthrown Olympus, and the gods admit defeat. But as the last of them fade, they visit the underworld. They bring back heroes who they know will keep Kronos from rising. They bring back heroes who will usher in the new era, exactly as it should be. But the mortal world has been left in disaster, and other heroes will come into play.
It has been four years since Tris Prior died. Tobias Eaton grieved her death, but now she turns up again, completely unharmed. She announces that she came back through the Doors of Death, once again left open. She tells everyone that the fight is not over, that their true enemies are the titans, giants, and demigods who turned their world upside down.
What no one realizes, though, is the true reason the genetic modifications began. A dangerous virus, called the Flare, sent out by Achilles Jackson, son of Apollo, mangled the human population, leaving the world desperate. Their first attempts to stifle the virus began with studying the DNA of the Immune, and attempting to modify the DNA of others to replicate the trait that made them immune. When that didn't work, two experiments began. The genetically impure were locked in the city of Chicago, in attempts to scavenge part of the human population and allow them to slowly recover from the failed genetic modifications. Then some of those who were immune were sent into a maze, to study their brains and use the information to find a cure. Including Thomas, who has just escaped from the Glade.
A crossover between three of my favorite series: The Divergent Trilogy, The Maze Runner Series, and PJO/HoO/TOA books.