Series of stories

[Thatbrunetchick]

Looking for an author/stories. I think if I remember correctly this author didn't write any standalone stories. All had chapters. The most memorable one was a girl gets kidnapped and a guy goes undercover to save her. They have sex in the place she's kidnapped and continue the relationship after they escape.
There might have been a age gap. One or more like she was seen like the little sister to the guy but now she's grown up and now he's interested.