Dark Beauty by Michelle Hardin

Right hand to one of the underworld’s most powerful crime bosses, Davina Delavigne is a woman conflicted. As a powerful individual of the underworld, she has done everything to make a name for herself and the place in which she comes from. DelACot. A secret society of elite assassins purposely hidden from the rest of the world.
Though always one to keep her focus on what she was taught was important, lately, she finds herself a bit … distracted. He’s tall, sinfully sexy, beautifully dangerous, and Davina doesn’t quite know what to do with the feelings she’s experiencing every time she’s in his presence.
Especially since those feelings are forbidden …
Underboss of the Salerno crime family, Lucca “Tick” Salerno is a man on a mission. When he’s not ruling his family with an iron fist, his focus is on winning the heart of a reluctant, unattainable beauty. Since the first moment he laid eyes on her, he wanted her. And, try as she might to convince him his feelings for her are one-sided, Lucca knows better. She wants him, too. No matter how long it takes, Lucca is determined to win the heart of the underworld’s Dark Beauty.