The Bad Time Broad (Merchant #4) by Chris Miller

A beautiful and mysterious woman with connections to the mob comes to see Sam Merchant with a dangerous offer and cash in hand. Merchant wants nothing to do with the mob, but as usual, he needs the money. And when he hears they're trafficking women out of one of their night clubs, he decides to take the job on the spot.

What he finds inside The Opal is utter depravity, and while no saint himself, Merchant is more than happy to mete out some justice. But when the mobsters get the drop on him, he discovers things are even more horrifying than he first thought. When creatures are stirring in the home of mobsters, things might get a little hairy.