Circus of the Dead Chronicles Book Five — Kimberly Loth

At first, it seems like no one died on the new moon, but when a mysterious letter shows up on Samuel's doorstep, Juliette has to race after him to find the body. They tear through the woods and find a ship wreck where one of Juliette's students has died. Samuel shares the letters he's received over the last couple of years and Juliette thinks she might know just how to find the culprit. But when her methods anger Samuel and he sets off on his own, it might be Juliette doing the rescuing this time...