Jason A. Adams 
Agonist [EPUB ebook] 

Loanshark Frank Powers lives by two simple philosophies:
Stay loyal to friends.
You sign, you’re mine.
Go back on your word, and Frank pays you a visit. If he likes you, and if he believes you, the syringe stays in his pocket.
Now Frank must become a savior instead of a shylock. A multitude of lives depend on his strength and old skills shaken free of mothballs.
Gangsters, guns, girls, and greed. Agonistrides a rollercoaster through the dips and dives of rage and redemption.