A ton of background information is revealed in this volume of Locke and Key, as the older Locke siblings discover a new key -

Spoiler

a key that lets them view the past, only not the too recent past, so they still remain unaware of the fact that Dodge switched bodies before he died

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We're taken through the history of the Keyhouse and the origins of some of the keys, as well as shown the final months of Rendell Locke and Lucas "Dodge" Caravaggio and their friends in high school. By the end of the volume, many questions are answered, but the peril feels closer than ever.