The Mystery of the Galilean Grindstone

At the end of the previous summer, Jupiter invited their new friend Mallory MacLeod to join the team as a Special Consultant. She's also been helping out at the Salvage Yard, so she, Jupiter, Pete, and Bob are all present when Uncle Titus returns from the Napa Valley with an intriguing artifact—a curious sandstone wheel.

The wheel appears to be a grindstone, engraved with the birth and death dates of Galileo Galilei, the brilliant Italian inventor and astronomer with ties to the powerful Medici family. When Uncle Titus suggests the wheel could be connected to rumors of a hidden treasure, the team quickly shifts gears to investigate. They travel to the old Victorian "calendar house" where the wheel was found—a hotel owned by Portuguese immigrants who are unaware of the house's mysterious past.

As it turns out, both the house and a nearby Franciscan monastery are brimming with Masonic symbols. The boys soon find themselves counting doors, rooms, and panes of glass, and deciphering cryptic letters in pigpen cipher that date back to 1890. When Mallory joins them and uncovers the startling connection between an ancient organization, the Illuminati, and the Masonic Order, the case takes on an added urgency.

But the puzzle isn't adding up. Is the Italian stonemason, Clemente DeLuca, as innocent as he seems ? Could the man writing a book about calendar houses be hiding his true intentions ? Are the brown cotton robes the monks wear acting as a disguise for one of them ? Locked inside the Tower Room, the team must work together to solve the mystery before it's too late. But the villains are closing in on the calendar house's secret—and they won't stop until it's theirs !

1. A Present From Uncle Titus
2. Some Very Intriguing Symbols
3. A Disagreeable Visit
4. Mallory Changes Her Travel Plans
5. Bob Solves A Puzzle
6. Some Very Exciting Letters
7. Castello Serreno
8. Suspicions And Clues
9. A Mysterious Sundial
10. A Meditation Upon A Missing Room
11. A Midnight Raid
12. Trapped In The Tower Room!
13. Jupiter Gets Discouraged
14. Pete Takes Charge
15. Folding Back The Cloak of Darkness
16. A Galilean Grindstone