Cathy’s Key (2008) is a novel continuing the storyline established in the first part of its series, Cathy's Book (2006). The story is written by Sean Stewart and Jordan Weisman, and illustrated by Cathy Briggs. As did its predecessor, the book takes the form of a 216 page journal written by the protagonist, Cathy Vickers. The book immediately picks up after book one of the series concludes, and follows Cathy in her quest to discover more about the mysterious and dangerous world of the immortals.