Series numeration from goodreads.com. "A Thomas Dunne book."
"Kat Stanford stumbles upon a hidden room in an abandoned wing at Honeychurch Hall. However, Kat's initial excitement soon ends in horror. There, lying on the cold, stone floor, Kat comes across the body of a young woman dressed in an Egyptian toga and wearing a tawdry fairground trinket around her broken neck. Suspicion falls on some of those who live at the Hall--both upstairs and down--and even those who are just been passing through. Matters come to a head as a killer lurks amid the aristocracy"-- Provided by publisher.