Pooh's Adventures of National Treasure: Book of Secrets is an upcoming sequel to Pooh's Adventures of National Treasure. It will appear in a near future.
Five days after the end of the Civil War, John Wilkes Booth and Michael O'Laughlen, both members of the Knights of the Golden Circle (KGC), enter a tavern and approach Thomas Gates to decode a message. Thomas recognizes the message as using the Playfair cipher and begins to translate it. While he does so, Booth leaves for Ford's Theatre to assassinate President Abraham Lincoln. Thomas solves the puzzle and realizes the men are still loyal to the Confederacy. A fight breaks out, and Thomas rips several pages from the diary and throws them in the fireplace. Thomas is shot, and the gunman retrieves only a page fragment.
Over 140 years later, Ben Gates is telling his great-great-grandfather's story at a Civilian Heroes conference. Black market dealer Mitch Wilkinson shows one of the 18 missing pages of John Wilkes Booth's diary, with Thomas Gates' name on it, convincing everyone that Thomas was not only a conspirator, but the grand architect of the Lincoln assassination. Ben sets out to prove the innocence of Thomas.
Using spectral imaging, Ben discovers a cipher pointing to Édouard Laboulaye hidden on the back of the diary page. He travels to Paris, where he finds a clue engraved on the torch of the scale model of the Statue of Liberty, referring to the two Resolute desks.
Ben then heads to London to look at the desk at Buckingham Palace with the help of his friend, Riley Poole, and estranged girlfriend, Abigail Chase. From the Queen's desk, he obtains an ancient wooden plank.
Meanwhile, Wilkinson broke into Patrick Gates' house and cloned Patrick's cell phone in order to track Ben's whereabouts. Wilkinson eventually obtains the wooden plank, but not before Ben manages to photograph the symbols carved into the plank.
At Ben's insistence, Patrick reluctantly asks his ex-wife and Ben's mother, Dr. Emily Appleton, for help in translating the symbols. She does so, but points out that some of the glyphs are partial, leading Ben to conclude another plank must be hidden in the other Resolute desk located in the Oval Office.
Ben and Abigail coax Abigail's new love interest, Connor, a curator for the White House, into letting them into the office to see the desk. Ben discovers that the second plank is missing, but he does find a stamp bearing the seal of the Book of Secrets. Riley tells Ben that the Book of Secrets contains documents collected by Presidents for Presidents' eyes only, covering such controversial subjects as the JFK assassination, Watergate, and Area 51.
Ben crashes the President's birthday party at Mount Vernon, with the hopes of showing the President a secret map drawn by President Washington of the Mount Vernon House and a secret escape tunnel under it. The President (Bruce Greenwood) is very intrigued by this and says to Ben they should go see it. They get to the secret tunnel under the House where they decipher a code and go in to the tunnel. Once inside Ben closes the tunnel door and explains his motive of proving his ancestor's innocence. Ben goes on to ask about the "President's Secret Book". The President sympathetically warns Ben that his actions will be interpreted as kidnapping unless Ben can prove the treasure's existence, and reveals the location of the book, in the Library of Congress, "where books are kept". He also gives Ben the book's index code and asks him to look at page 47.
Ben calls Riley and Abigail and has them meet him at the Library of Congress. They make their way to a locked door where Ben uses the second code the President gave him. They are all rushing to find it and while doing so see it's not there, but as Ben pulls down a book where it should be, happens to see a secret locked panel. Ben uses the book's index code to unlock it and there is the President's book. They find the page with the information about the missing plank and Ben reads an entry by President Coolidge, who found the plank in 1924, had it destroyed, and commissioned Gutzon Borglum to carve Mount Rushmore to erase the map's landmarks in order to protect the treasure; while reading they hear police cars coming. Ben tells Abigail and Riley to go and he takes a picture of the plank; Ben flips to page 47 and takes a picture of that as well(while never showing what's actually on page 47). Cops and FBI are now flooding the library to find Ben, while Abigail and Riley are making their escape. Ben manages to get out and jump into Abigail's fleeing SUV while being chased by cops. Ben then sends the picture of the plank to his dad and tells him he must get it translated by Ben's mom.
Before Patrick can get to Emily's office for the translation, Mitch arrives and tells her he needs the plank translated. Before she reads it Mitch gets a call telling him Patrick is on his way to her office; Mitch orders Emily to lie and get rid of him. Emily translates the plank but lied about the last symbol; after some words are exchanged between Emily and Patrick, Patrick leaves. Mitch walks back in and shows her a letter from the Queen of England to one of his relatives during the Civil War and tells her that the letter is needed along with the planks to actually find the treasure, then burns it. Mitch orders her to get her coat and leave with him.
Ben, Riley, Abigail, and Patrick head to Mount Rushmore where they meet Mitch, who has Ben's mother. Ben knew she was in trouble by the translation Emily gave to Patrick by the last symbol she read to him. Ben tells Mitch they can work together but his gun and men must stay behind. Mitch agrees and he helps them find the entrance of a cave from the writings in his family's secret Queen letter. They enter the cave and start looking for clues to find their way to the legendary Native American city of gold, Cíbola. Along the way they encounter several traps, and Patrick and Emily get separated from the rest. Eventually, they find the city of solid gold beneath Mount Rushmore and all are reunited. While everyone is looking around at it's beauty and wonder, water starts pouring in. In order to escape the water and drowning, one person has to stay behind to hold open the escape hatch. Mitch demands that he leaves while Ben stays to hold it open or Abigail gets hurt. Ben agrees and Mitch helps him open the hatch once more. While Ben holds it, they all swim out but before Mitch can go Ben is thrown from holding it and gets his arm stuck. This forces Mitch to save Ben and sacrifice himself, asking Ben to give him the credit for finding the treasure.
Once out Ben calls Agent Sadusky and tells him they found the treasure. Ben, Abigail and Riley are escorted to see the President. The President tells the secret service Ben didn't kidnap him and that he helped him get out of the tunnel. The President shows Ben the next days newspaper and that it clears his family's name. Ben also ensures Mitch receives joint credit for the find. The President asks Ben about his previous request, looking at page 47 of the Secret Book; he replies that what was written on the page is "life changing". Meanwhile, Emily is overseeing the treasure and relic removal with Patrick by her side. While Riley is asked by a pretty fan of his book for his autograph, Ben and Abigail decide to move back in together. Then back in Washington, Riley is walking down his street and sees a new red Ferrari. As he goes to look, he sees an envelope with his name on it; he opens it and finds the keys with a note from the President that says: "tax free". He jumps in and starts his new car up. While listening to it purr, he says "I love this car", and puts it in drive and hits the gas; while really being in reverse and flies back into a parked car.