Archangel is a YA dystopian novel set in Chicago and Detroit about 200 years in the future. It is a world of enormous technical and material inequality. The ruling are well educated and have electric-powered vehicles, the ruled have horses and carts and cannot read. The great human cities, like Chicago and Detroit, are largely ruins. Many of the tower blocks have no external walls or electricity but people live in them anyway.
CH wanted the cover to be designed around a symbol, as in The Hunger Games, or Divergent, or Legend. The symbol should be Triskele.