So good! It's up there with my favorite Greg Egans! In Clockwork Rocket and Incandescence style, the plot revolves around research in a setting where something fundamental is different. This time we are in a world full of body horror. Your arm can just decide to leave you. The people of this world are used to this, so the book sets off from this baseline and heads for the ever weirder.

The characters are the typical Greg Egan fare: level-headed and reasonable to the extreme. In some stories these come off as bland, but here I really loved them. Being level-headed and reasonable in this world comes off as heroic.

The book is a fun variation on the Bechdel test. I was 20% of the way through when I realized all the characters in this world are women. (In fact all creatures are female.)

I love the way clues are dropped for an important mystery. You are clued in gradually. Someone will figure it out on the first hint, someone will take five hints. No matter where you figure it out, it feels like you solved the puzzle. I suppose it's a common approach, but I found it done well here. All the flashbacks are paced well. Everything works great. There's enough drama left even for the last pages, and I loved how the conclusion wrapped up every thread. Very satisfying.

While the whole book is well made, the unique part is the research fantasy. It's not extremely technical. But it's still fun, and makes you think about how researchers have figured out similar things in our world.