Mr. Penumbra tells Clay, Kat and Neel the Story of the cult.
"The cult is based New York City. Every member must solve the Founders Puzzle (the one you solved) to get in. Every member writes their own book, and gives it to another member to keep safe. The main objective of this cult is to decode a book that may hold he secret to immortality."
Penumbra then suggests that Clay should scan a copy of this book, and should use software to try and decode it.
"So far, we have been unsuccessful."
Clay and Kat hold a big event, inviting all of the members of the cult to see him and a bunch of other computer geniuses from Google to try and crack the code. They fail, and Penumbra disappears again.
It didn't work......
Where's Mr. Penumbra?
In order to find where Mr. Penumbra is hiding, Clay must find punches (a metal tool used for stamping letters for old books). He finds them in an old storage unit.
Here they are!
On his way back home he listens to his books on tape. The author of those books was a member of the cult. Clay finds a secret message hiding the words. He finds a way to decode the book!
So the code isn't in the writing itself, it's in the letters!
Clay finds Penumbra, and invites him to another big event where he decodes the text. He zooms in on the letters and finds text. However, the books does not hold the secret to immortality. It is just a memoir of the person who wrote it.