Kingpin by Alexa Riley

Thea James is scraping by and trying to make a decent life for herself. She keeps her nose clean and stays out of trouble, trying to do what she can to pay the bills. One night on her way home she becomes a witness to a murder.
Suddenly, with the shot of a bullet, she’s thrust into a world she had no idea existed. But what’s Thea to do when the darkness that could swallow her is exactly where she wants to go?

Salvatore Costello is the boss in the Los Angeles mafia.

He’s in charge of everything, and that includes who he allows in his inner circle. He’s spent his whole life not letting anyone close to him because he knows what the consequences could be. But one night changes everything. She’s a witness and she needs to be taken care of, but after one touch, he’s redefining what that means. Is she strong enough to lead his empire? Will she be ripe enough to give birth to one?