Phryne Fisher is holidaying at Cave House, a Gothic mansion in the heart of the Victorian mountain country, but the peaceful country surroundings mask danger. Her host is receiving death threats, lethal traps are set without explanation around the house, and the maid is found strangled to death. Phryne's search for answers takes her deep into the dungeons of the house and of the limestone Buchan caves, but what will she find this time?