A Secret History by Donna Tartt

Richard Papen, a vaguely unhappy young man from California, decides on a whim to apply for Hampden College in Vermont. When he arrives, he notices a group of five eccentric students, Classic majors, who seem completely separate from the rest of the college. Because he has studied Greek for two years already, Richard is tempted to join them. Although he is told by Jullian, the professor who is the head of the Classics department, selects his students by methods nobody can quite figure out. But Richard does end up joining the circle.
We are told in the prologue of The Secret History there has been a murder-a student named Edmund also known as Bunny is dead. We are told who is responsible for his death, so the who did it is never the mystery. But the mystery is why they did it; which is why The Secret History is unique in that the mystery is about the exact circumstances that led to the murder. Which is why I believe that The Secret History won't disappoint.