This book has a kidnapping trope and is definitely dark but not overly so. It focuses more on psychological and emotional aspects, I suppose, rather than descriptions of graphic violent scenes. I kind of appreciated that, because I'm not a huge fan of super dark and twisted. 
 There is a pretty interesting back story involving two main characters and the book jumps between the past and the present. I very much enjoy stories with the flashbacks from the past because I do so lurve good character development. This was my second book by Leylah Attar and her writing continues to surprise and... please me. Ok, that sounded creepy. lol 
 If you haven't yet read 
 I suggest you do so :p