Methinks Scholastic must have had in mind to create a Magic-Tree-House-ish series for the next age group up. Seems they are succeeding. Middle Dude barely remembers to breathe when he’s inhaling these books. I’m skimming along loosely just to keep up with the outline of the story. Big Dude is still in book two (but, y’know, he actually tries to solve some of the riddles/clues).
Middle Dude has solved several of the clues provided inside the covers; I’ve only solved a couple.
Here's a clue for you. You're welcome. ;-)