To find this cache, you will need to use a book cipher known as the “Arnold Cipher,” named after the infamous turncoat, General Benedict Arnold. Arnold used this cipher to send coded messages to the British military during the Revolutionary War.
The Arnold Cipher is based on three-numbered sets, and requires a book to decode. In each set of numbers, the first number indicates a page of the book, the second number indicates a line on the page (counting down from the top), and the third number indicates a word in the line (counting in from the left).
To get started, go to the posted coordinates to find the name of a book. Locate that book in the library for the second stage, and use the first set of numbers below. That will give you a clue where to go for the third stage. At the third stage, you will likely find two versions of the same text. Select one, and use the corresponding second set of numbers. That will send you to your final location in the library. (Both versions of Stage 3 will give the same message; there is no need to decode both.)
Stage 2:
[424, 10, 11]
[400, 1, 1]
[580, 29, 10]
[331, 37, 7]
[403, 14, 3]
Stage 3: Penguin
[84, 27, 1]
[60, 2, 6]
[115, 31, 3]
[57, 29, 9]
[34, 20, 1]
[74, 14, 7]
[63, 17, 5]
-OR-
Stage 3: Popular Library
[66, 9, 1]
[48, 10, 6]
[88, 41, 5]
[46, 28, 8]
[29, 18, 3]
[58, 27, 7]
[50, 30, 5]