Raven Mysteries: Diamonds and Doom: Book 6 by Marcus Sedgwick
Join the wonderfully weird Otherhand family and their faithful guardian, Edgar the raven, and discover the dark secrets of Castle Otherhand. In the sixth of the Raven Mysteries, all manner of disaster descends on Castle Otherhand; weirdness abounds, the family are on the verge of being thrown out of their own home, and there's still no sign of the fabled treasure of the Otherhand. Worse still, there's no sign of Edgar, either. So will it be diamonds or doom for the Otherhands?