National Treasure: Book of Secrets (2007)

Five days after the end of the Civil War, John Wilkes Booth and Michael O’Laughlen, both members of the KGC, approach Thomas Gates to decode a message copied into Booth’s diary. Thomas recognizes the message as a Playfair cipher, and translates it while Booth departs for Ford’s Theatre to assassinate President Abraham Lincoln. Thomas solves the puzzle, realizes Booth and O’Laughlen are trying to help the Confederacy, and rips the cipher’s pages from the diary to burn them. O’Laughlen shoots Thomas and flees with the one surviving page fragment, and a dying Thomas tells his son Charles the keyword for the cipher.

Over 140 years later, famed treasure-hunter Ben Gates tells Thomas’ story at a Civilian Heroes conference. Black market dealer Mitch Wilkinson produces the page fragment, with Thomas Gates’ name next to those of Mary Surratt and Dr. Samuel Mudd. The public believes Thomas helped kill Lincoln, and Ben and his father Patrick set out to disprove it. Using spectral imaging, Ben discovers traces of the cipher on the diary page; when solved using the keyword, it points to the smaller Statue of Liberty in Paris. Traveling there, Ben and his friend Riley Poole discover an engraving referencing the Resolute desks. They head to London, reluctantly recruiting Ben’s estranged girlfriend, Dr. Abigail Chase, along the way. Ben and Abigail sneak a peek at the Buckingham Palace desk, and obtain a Pre-Columbian carved plank from a secret drawer.