One example is Fatality, a fascinating story about a girl who steals back her diary from the police before they can read it or use it as evidence in a murder case. The reader keeps wondering what the secret information in the diary was until the very end of the book.
The book is also about relationships between friends and family, which play an important part in the plot.
Cooney's books are a bit too edgy for children, but appropriate for teen girls who like adventure. They also make readers think about what things in life are really important.