Ascension by A.S. Fenichel

When demons threaten London, even ladies must answer the call...

Lord Gabriel Thurston returns home from war to find his fiancée much changed. She's grown from a sweet girl into a mysterious woman who guards her dark secrets well. When he sees her sneaking away from a ball, he's convinced it's for a lovers' rendezvous. Following her to London's slums, Gabriel watches in horror as his fiancée ruthlessly slays a man.

Lady Belinda Clayton's only concern was her dress for the next ball--until demons nearly killed her, and a group of Demon Hunters saved her life. Now, a lady by day, and a demon hunter by night, she knows where her duty lies. Ending her betrothal is the best way to protect Gabriel from death at a demon's hands.

Gabriel soon realizes, like him, Belinda has been fighting for her country. He joins in the fight, determined to show her that their love can endure--even at the gates of Hell.