The Mysterious Moonstone. 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. The Spy's Secret. In their second trip through the enchanted library, the new key lands Cleo and Evan in the middle of a spy story, where their impossible mission is to stop a traitor who calls himself Viper--and they find themselves working with the replacement librarian, Ms. Crowley, whose exact role in their adventures is becoming increasingly mysterious.

"Flip this book to unlock another adventure"--Cover. Titles taken from separate title pages; works bound back to back and inverted.