Gideon Nav is a snarky teenage girl, abandoned as a baby at the Ninth House of necromancy, secluded on a small, dreary planet on the outskirts of the Dominicus star system. Her possessions are few, but they include a) a passionate and mutual hatred of Harrowhawk Nonagesimus, the Ninth House\’s heir and most skilled necromancer, b) a fervent desire to escape the Ninth House and do something with her life besides be constantly tormented by Harrow, and c) a large sword and the skills (and, as a point of particular pride for Gideon, biceps) to use it well. A gathering of representatives from the necromantic Houses may give Gideon the chance she\’s been looking for – if she can survive working with Harrow.
The gathering\’s goals are unclear and the rules seem few, and the venue is an ancient ruin filled with locked doors. The doors conceal secrets and dangers, hinting at the potential to attain vast necromantic power. Each of the Houses have not only their own style of necromancy but their own secrets to keep as well, and so the assembly of adepts and their cavaliers quickly ignites into intrigue, as the Houses compete and cooperate to try to solve the mysteries to which they have been summoned.
The setting is a brilliant fusion of sci-fi and fantasy, interplanetary travel and research laboratories set against reanimated skeletons and corpse divination, reminiscent of Warhammer 40K or the Craft Sequence.  Gideon herself is an entertaining viewpoint character, sarcastic and sharp-tongued, but clearly out of her depth among the more properly-trained cavaliers of the other Houses; that plus her past gives her both a drive to prove herself and a deep sense of insecurity.  Her and Harrow\’s enmity is tied into their past as well, and their need to figure out how to work together despite their history drives a sympathetic character arc that interacts well with the mystery plot. The end of the book tees up plot elements for the sequel – Harrow the Ninth, out later this year – but Gideon the Ninth still comes to a satisfying resolution on its own, tying the plot and character arcs together in a tense and exciting climax.