Echoes of Angels — Matt Larkin

More than three thousand years ago Angels saved humanity from destruction, but Earth was lost. The Angels spread humanity across the stars and ruled the universe for twenty-five hundred years. Then they vanished. Angelologist Rachel Jordan has come to the hellish world of Gehenna in search of a lost relic said to hold all the knowledge of the angels. But other factions seek it for themselves, and religious zealots will stop at nothing to keep it safe.