The Gutter Prayer book by Gareth Ryder-Hanrahan

A group of three young thieves are pulled into a centuries old magical war between ancient beings, mages, and humanity in this wildly original debut epic fantasy.

The city has always been. The city must finally end.

When three thieves—an orphan, a ghoul, and a cursed man—are betrayed by the master of the thieves guild, their quest for revenge uncovers dark truths about their city and exposes a dangerous conspiracy, the seeds of which were sown long before they were born.

Cari is a drifter whose past and future are darker than she can know.
Rat is a Ghoul, whose people haunt the city's underworld.
Spar is a Stone Man, subject to a terrible disease that is slowly petrifying his flesh.

Chance has brought them together, but their friendship could be all that stands in the way of total armageddon.