Mystery Novels for School?

I really need help finding good books to read for school. My school instituted this program called "Accelerated Reader". If you haven't heard about this program, basically a student will read a book, take a test on the book, and earn points based on how well they did on the test, and you have to earn a certain number of points every semester. Anyway, I need help finding some books to read. I really like mystery novels. I liked the Harry Potter books, the Da Vinci Code, and a manga series called Death Note because they were all mysteries. However, our teacher asked us at the beginning of the year which of us had read the Harry Potter books, and those that said yes can't take a test on it. I took the test on the Da Vinci Code already, and Death Note is not available for tests (only certain books have tests for them). Any suggestions?