Blackbriar — William Sleator

Danny is intrigued by Blackbriar's eerie, haunted atmosphere. And as he investigates the house's past and its connection with the strange fires sometimes seen on nearby ancient burial mounds, Blackbriar and its previous occupants exert a strange influence on him. Until, on the night of the full moon, while the bonfires are burning, and the naked figures are dancing, and his companions have been kidnapped…Danny faces to most horrifying night of his life.