THE LUMINOUS DEAD by Caitlin Starling

A new review over at Tor.com:

[The] setup looks, in a nutshell, like survival horror: Gyre striving to survive in an inimical environment and fighting to maintain her autonomy against a handler who should be on her side.

Fortunately for us, Starling has written a deeper, richer, and more complicated story. The Luminous Dead is a story of two isolated people who have been defined (and who have defined themselves) by traumatic losses in their childhoods as they open up to each other in the darkness of a cave whose depths may prove unsurvivable.