The New York Museum of Natural History has reopened, and security guard Larry Daley (Ben Stiller) led Teddy Roosevelt (Robin Williams) to plan a wonderful opening performance. Unexpectedly, not long after the performance, Teddy, the monkeys and others fell into chaos, and all the partners in the museum made a scene at the venue, which made Larry very anxious. Afterwards, he discovered that the resurrection golden tablet was being corroded by green substances, and this situation seemed to cause the madness of the collections. Larry searched for information and concluded that there was an unknown secret behind the golden tablet. In order to prevent the spread of chaos, he decided to go to the British Museum to seek help from Pharaoh Akamanra's father, and of course the pile of funny collections followed. On the way, they met Sir Lancelot, a knight of the round table, and got separated from Octavian and other partners. The long-lost wonderful adventure unfolded in the British Museum under the night...