Readers were first introduced to Charlie and (somewhat) Gabriel in Rock Addiction. We got to see the start of Charlie and Gabriel's tug-of-war from Molly's perspective which perfectly set up for me wanting to get the full story told. 
 I'm glad we didn't have to wait too long for this. 
 It's clear in Rock Addiction that something bad happened to Charlie in the past, in a relationship. I don't think I understood how bad it actually was until reading Rock Hard. 
 Charlie is very intimidated by new boss Gabriel Bishop. Not only was he a star rugby player, but now he's making waves in the business world and he's quite easy to look at too. When she's promoted to his personal assistant, Charlie doesn't know how she's going to work around someone with such coiled strength, but she can't let the opportunity pass. 
 Gabriel Bishop is used to getting what he wants. He worked hard playing rugby and when that couldn't go on any longer (due to an injury) he built himself up in the business world. Right from the start he's captivated by Charlotte. He doesn't understand why she shies away from him but he's determined to find out. 
 I liked the pacing in Rock Hard more than in Rock Addiction. I don't know if the set-up of this story in the previous story helped, but it seemed like things flowed a little better. Molly and Fox's relationship just seemed to take off right from the start, but with Charlotte's past issues Nalini Singh was careful to give things their time to develop which, for me, worked better. 
 Gabriel was great for Charlotte. He was understanding, and he wanted to help her. He would push her in just the right ways, never trying to overwhelm her. 
 One of the only things that I could say as a somewhat negative to the story is that Nalini Singh tries to throw in personal issues for Gabriel to work through. I understand in the real world and in real relationships things are two-sided. I think in order to compensate for Charlotte having to deal with her past, Nalini Singh tried to give Gabriel something too. But because what Charlotte has to deal with is so big, Gabriel's personal matters don't get justice done for them. 
 I'll admit, however much I wanted to read Gabriel and Charlotte's story, I was surprised that Nalini Singh veered focus away from the other guys in Schoolboy Choir for this story. I know she'll get back to them in books to come because they're all waiting to have their HEA's, but by going away from them, Nalini Singh managed to make me want stories for Gabriel's family whom we meet in Rock Hard. A couple of them I could definitely see getting at least a novella. 
 Regardless, even if you were a little on the fence about your feelings regarding Rock Addiction, I would definitely give Rock Hard a try.