This Gilded Abyss, by Rebecca Thorne

This Gilded Abyss is a horror fantasy novel, written by Rebecca Thorne, also known for her series of cozy novels Tomes & Tea. Really different from her other novels, in this case, we have a horror story set in a world with Bioshock vibes, tickling several boxes on what I look for in a book.

In this story, we are going to be following Sergeant Nix, a soldier who wants to forget her traumatic past, as she lost one of her best friends years ago, Quian. When Subarch Kessandra, one of the favourite royals of Valkesh, and Nix's ex, requests Nix's protection to investigate a massacre in the city of Fall, a submarine place, she immediately refuses; Kess is part of that past she's trying to flee from.
Using her influence, Kessandra manages to enroll Nix in this mission, getting both aboard the Luminosity, a submersible. But once the truth is revealed, this luxury vehicle becomes a dangerous place, as Kess is not really investigating the massacre, but the cause of it: a illness that creates a violent rage in its victims, and that seems to have been spreading in the Luminosity. Our characters won't have any other option than leaving the past behind and trusting each other if they want to survive until the submersible is docked into Fall.

With this premise, we also have an enemies-to-lovers relationship in the figures of Nix and Kess, influenced by their shared past. Both are similar in some aspects, especially in how both are super fixated on what they think, and that makes their personalities clash. Nix is suffering guilt and anger due to Quian's death, and partly, she blames Kessandra; overcoming this trauma will be key to survival.
On the other hand, Kessandra is one of the most loved royals, and she's trying to combat this mysterious disease, which seems to be related to Ichoron. Her position seems powerful, but in reality, she has taken several risks to discover the origin of the disease, becoming the target of a complot to eliminate her.

Thorne weaves a credible relationship between our two characters, using the tension created by the situation to make it evolve. I would say it's not especially spicy in terms of romance, but if you like to read some romance, you won't be disappointed by this sapphic one.

Another aspect that I feel Thorne nailed is the horror atmosphere. Using a closed location, the tension is enhanced greatly, and I would say the existence of an "invisible threat", such as a disease, is certainly a success; vibes are really similar to the ones I experienced playing Prey (by Arkane Studios).

Talking about the pacing, I would qualify it as relatively slow at the start, taking its time to introduce the world and the relationships among the characters, which will be central to the plot. Once we are aboard the Luminosity, it accelerates to the point you are just devouring the pages.

My other gripe is the ending, as I think it could have worked better as a standalone, instead of using an open ending, which prepares for a trilogy. Said that, This Gilded Abyss is an excellent book, even when you take those minor things into account; a total recommendation if you like horror in your fantasy. Extra points for the steampunk vibes.