This book checks off a lot of boxes: fantasy goth aesthetic but set in space; queer in the sense of both gay and weird; spooky and gory but full of Buffy-esque quips. In the opening scene we meet Gideon, an orphan raised in a horrible moldy tomb of a planet called the Ninth House. Gideon has lived 18 miserable years in this dark, decrepit hole and plans to get out, once and for all. She's set up an elaborate escape scheme and plans to enlist in the Cohort, distinguish herself on the war's front lines, and get piled with glory, hot babes, and cold hard cash. The one thing standing in her way is Harrowhawk, a necromancer bone witch, first daughter of and heir to the Ninth House. Harrowhawk is a year younger than Gideon and they grew up as the only two living children on the planet. They have been fighting, kicking, screaming, hating and plotting against each other since they could walk. But Harrowhawk has been called to the service of the Emperor, and each necromancer needs a swordsman cavalier. Gideon is the only option and so the enemies much become distrustful allies to solve a murderous challenge on the the Emperor's home planet. If they survive, they will be raised to the highest positions of the empire. If they loose, their souls will probably be trapped in a hellish prison forever. No pressure.

Edit in 2022: I re-listened to this a second time as audiobook and enjoyed it even more on a second pass! This book deeply rewards a re-read, when all of the weird twisty parts of the mystery actually make sense.