I was torn actually between starting that one next and Red Sister. Then I saw some negative comments about Gideon that made me hesitate, so your recommendation is actually much appreciated.
No actually they were saying that the characters were unlikeable and complaining that it apparently has a downbeat ending, neither of which I was feeling up to.
I think the blurb sets up a bad set of expectations. "Lesbian necromancers in space" makes it seem like a Sci-Fi/Fantasy LGBT+ romance novel. Instead you get a mystery in a setting that is only technically science-fantasy with a vague romance side plot.