The Likeness by Tana French
Detective Cassie Maddox gets called to a crime scene where the murder victim bears a startling resemblence to herself. This gives her old boss Frank an idea - if Cassie goes undercover as the victim then they might find out who killed her. This puts Cassie into a pretty dangerous position, impersonating someone who's actually dead but who the police have said is just injured, to a houseful of friends who may or may not have had something to do with killing her. It's a fascinating concept and the plot is pretty intriguing too as Cassie gets more and more involved with her "housemates" and their laid-back Bohemian lifestyle. I'm not going to say anymore about the plot as it would only spoil it for you. Suffice to say that this was another big hit and I'm on a kind of roll here with good books, even if I am only 3 books into what is looking like a bigger challenge than it seemed three weeks ago.!