So many things are revealed in this volume dealing with major back story behind the house. The characters we have been seeing now and then are now tied to the story and we finally come to know the origin of the keys and Mr. Locke's role in it. 
 All references - people, photographs, anecdotes are all justified and reinstated in this volume and it clicks into place perfectly. Hill takes time to unravel the story bit by bit answering lingering questions from previous volumes. 
 Now its just a matter of time till it all ends.