The Mysterious Moonstone, Paperback

Cleo and Evan have a secret. A collection of books so dangerous they are locked up tight. A friend has vanished inside the pages of one of them. It's up to them to find the key that will set her free.
A PRICELESS DIAMOND...STOLEN
When Cleo and Evan go undercover to help a rookie detective interview a mansion full of suspects, nothing is as it seems. They must catch the crook -- and find the right key -- or they could be trapped inside this mystery forever...