Days after Commander Seraphine Vey ends a twenty-year civil war in Mexico’s volcanic highlands, an earthquake exposes a hidden Mexica archive beneath Vespra just as the Cathedral of the Revenants begins its once-a-century return. When Seraphine’s daughter Elianor becomes bound to the archive’s living black book, Seraphine and her secretive chaplain Lucien must enter the Cathedral’s seven chambers to save her—only to discover they have been summoned to answer for the dead Vespra erased.