Dragon and his grandmother

"When three soldiers leave the battle to hide in a field, a dragon rescues them . . . but it comes with consequences. Dragon offers them safety only if they serve him for seven years. To be set free they must answer a riddle. Will the soldiers gain their freedom, or will they be servants of the Dragon forever? This is a grim retelling of 'The Devil and His Grandmother,' an 1800's English tale adapted by the Brothers Grimm"--Back cover.