In the Egypt-inspired kingdom of Ashdod, the slave glassworker Tirzah has spent years laboring on Threshold, a vast glass pyramid the ruling Magi believe will open a gateway to Infinity and union with the One. When the structure is finally activated, it instead admits the demonic Nzame into the world, turning the land to stone and black glass. Tirzah's hidden gift for hearing the spirits within glass, and her uneasy bond with her former master Boaz, may be all that stands against it.
Summary by Loreful, from public sources