Justice Buried

I received a copy of this book from NetGalley. One hundred years ago, The Great Sickness or Cleansing wiped out everyone but the people in 3 cities. The city of Asphodel has been underground since then. They never go above ground, have never seen the sun, or anything. Now, according to prophecy, Lexan and Astrea are supposed to lead their people out of Asphodel and go above now that the Great Sickness has passed. Was the Great Sickness an act of God, or was it man-made? I enjoyed this book, although it completely left me hanging and wanting more.