The Crystal Cave; The Hollow Hills; Airs Above The Ground; Wildfire At Midnight: Mary StewartThis omnibus volume contains: The Crystal Cave: the enthralling tale of Merlin, enchanter in the days of King Arthur. The Hollow Hills: The saga of Arthur's rise to power. Airs Above The Ground: A humourous and dramatic tale of a young couple who get caught up in the dangerous life of an Austrian circus. Wildfire at Midnight: A young divorcee on holiday in Scotland is caught up in a mysterious ritual murder and the complex relationships of her fellow