Dangerous Innocence by Cora Reilly

Aislinn Killeen is a good girl. When her sister goes missing during a trip to New York, Aislinn leaves her hometown Dublin behind to search for her. She finds shelter with her uncle, a priest in the city’s biggest Irish-catholic parish and also the confessor for the Irish mob. Her investigations soon lead her to the criminal underworld and one of its major players: Lorcan Devaney.

Lorcan Devaney’s reign is brutal, his temper feared, and his patience non-existent.
Aislinn is sure he’s the man who knows what happened to her sister. She realizes too late that attracting the attention of a man like Lorcan is a horrible idea. When secrets from her family’s past are revealed, she’s forced to marry the man who might be responsible for her sister’s disappearance.
Will she find her sister and escape the unwanted marriage, or will she be the second Killeen to disappear?