Nevernight

A young assassin joins a group of killers in a place where three suns almost never set with the intention of exacting revenge on the entities that killed her family.

Mia Corvere, the daughter of a hanged traitor, barely makes it out of her father's abortive uprising alive. Hunted by the Senate and her father's erstwhile allies, she hides in a city made of a dead god's bones, alone and without friends. However, her ability to communicate with shadows brings her face-to-face with a retired murderer and a destiny she never would have imagined.

Mia is now an apprentice of the Red Church, the deadliest assassination group in the Republic. She will become a member of the Blades of the Lady of Blessed Murder and go one step closer to getting the retribution she so desperately wants if she defeats her other pupils in competitions using steel, poison, and the subtle arts. However, there's a murderer on the loose in the Church's corridors, Mia's past's gory secrets are coming back to haunt her, and a conspiracy to destroy the whole congregation is developing in the shadows she loves so well.

Will she even make it through initiation, much less exact her retribution?