The Bomb Maker's Apprentice

A hired assassin killed Richard Barton's younger brother. While wading through his own grief, Richard's parents pressure him to find this killer and bring closure to the family tragedy. To do so Richard must walk a dark path and join a criminal organization.
It takes months of violent tests and trials for Richard to finally get inside as part of the team. As an ex-soldier, Richard thinks he's witnessed the worst of humanity, but he's wrong. The brutality he now sees, surrounded by villains, is more horrible than he could have imagined.
If Richard wants justice, he might have to become monstrous himself. More than that, he must be careful and not ask too many questions because the wrong question could mean death.