Can you crack the case with six clues or less? Moon Hollow's town library is a favorite spot for the Mysterious Four. But when the strange, masonic glyphs that decorate the building prove to be a secret code, they discover there's more than books hidden away inside. Embarking on a treasure hunt, Viola, Sylvester, Rosie, and Woodrow must run a gauntlet of mysteries and puzzles--and readers are invited to guess alongside them with every new clue they uncover. Each book comes with an exclusive code so that readers can download a FREE copy of the e-book . . . which includes an extra mystery unavailable anywhere else!