There is a problem to be solved in mystery stories - sometimes these are solved by police, detectives, spies and, in lots of stories, young adults, who are the main characters in the story.
Into the dark by 
What I saw and how I lied by 
Black rabbit summer by 
Blaze of Glory by As well as these suggestions, you cfan also look at the library catalogue here, where you can do a subject search, using words used to describe this genre.
The Glass Books of the Dream Eaters by 
Miss Peregrine's Home for Peculiar Children by 
