Hell's Acre. Hell's Acre, #1

Gemma Dove arrives in New Rome with a small independence and a burning desire: to gain revenge upon those who murdered her parents and drove her beloved aunt to a premature death. The city is a dangerous place, but Gemma has her own secret skills and isn't afraid to use them. She longs to complete her vengeance and return to her safe, beautiful estate across the Channel, but fate has other ideas. His name for now is Avery Black, but they call him the Rook.
The young Hellion has sunk himself in vice and treachery, and he knows there's more to Miss Dove than meets the eye. He also knows she's playing a dangerous game, one which will end in her death-unless he takes a hand in matters. It might even be connected to his own vengeance against the Priory, but that's fast becoming a secondary consideration. Under soot-stained skies and flickering gaslamps, from the crowd of thieves and gin-soaked tenements to the glittering whirl of Society, plans, treachery, and counter-betrayal are afoot.
Gemma and Avery can deal the Priory a stinging defeat, but that ancient organization has its own plans for Miss Dove, and the Rook might be her only defense.