The Ninth Guest (Jacob Lane 4)

Jacob Lane is a ten-year-old girl who's spent her life unaware of her magical heritage. After being sent to Darkbrook, a school of magic, supernatural mysteries seem to spring to life all around her and her new friends. When Jacob's friend Ophelia's family decides to open up their castle for guests, amateur paranormal sleuth Jacob Lane is invited to join in on the fun. "Spend the night in a vampire's castle and live to tell the tale!" is supposed to be a fundraiser to help Ophelia's family pay the bills. Heating a castle costs quite a bit, after all. But, after the truth of an old secret is uncovered, what began as an innocent business venture soon turns deadly when vampire hunters get involved. For years, the vampire hunters have had only one goal: To destroy all vampires. With the help of a new friend, Jacob and Ophelia must work together to save the entire VonBriggle family from extinction.