A Harmony of Hells. The Paris Trilogy, #3

A poet haunted by grief. A lover marked by blood. A sister silenced behind asylum walls. In the decadent heart of fin de siècle Paris, Averill Charron makes a devil's bargain. To rescue his sister-locked away by their father-he turns to the last man he should trust, Blaise Dancier, the crime lord who once ordered his death. No longer enemies. Now they are lovers. Together they descend into the underworld-back alleys and brothels, cabarets and crypts-chasing whispers that lead only to deception and death.
Even as they hunt for her, Jeanette fights for her freedom. But escape only leads to recapture. Once again, she's trapped in a world where only dreams of forbidden love and the promise of revenge keep her sane. Their paths converge in Venice, during the revelry of Carnevale, where every mask conceals a threat. In a world ruled by power, madness, and betrayal, love may be the final sacrifice.