The character in this book is equated to be a female Jack Reacher, and although I found them similar in the attitude they have toward whatever violence is necessary to accomplish the goal, I didn't enjoy this nearly as much as any of Lee Child's books. I certainly don't feel any need to read any further novels if this ends up being a series.
The book is non-stop action, as well as non-stop gore and violence. There is also drug use in the story as well.
As someone who has been a victim of domestic violence, I'm not a fan of the storyline that has Nikki reciprocating to the abuser whatever he has doled out to the woman that he abused. I'm sure some women may dream of this happening, I'm one of those who doesn't believe that two wrongs make a right. And knowing that abuse is caused by a need to control, I don't think getting beaten up would really make a difference - you have to change the abuser's entire way of looking and life and responding to others.