Voices in Stone (Paperback)

Isis, the daughter of a charlatan psychic, can see ghosts--including that of her dead little sister, Angel. Gray is the son of a UFO-chasing conspiracy theorist. The two became friends over the summer, when they fought a deadly ghost together. So why is Gray now ignoring Isis at school? On a field-trip to a local mine, the pupils are "accidentally" coated in dust, which has very odd side-effects. Could this be related to the ley lines and standing stones which have been calling to Isis with strange, ghostly voices?