Night at the Museum Plot

Night at the Museum Plot (Short Version)

Larry Daley is a divorced father who is unable to keep a stable job, the bulk of them being failed business ventures. He is desperate to win the support of his son Nick whom he fears is beginning to look up to his more successful future stepfather, Don , a bond trader on Wall Street. Larry therefore applies for a job at the American Museum of Natural History, where he is assigned as a night guard.
The three elder (soon to be retired) night guards, Cecil, Gus, and Reginald , give him a quick tour, advise him to leave some of the lights on, and warn him not to let anything "in . . . or out", which Larry meets with humorous skepticism. They also leave some odd instructions for him.
Once night comes, Larry discovers that the museum exhibits come to life. Larry barely manages to survive through the night. First, he discovers a Tyrannosaurus rex drinking from a water fountain; Larry distracts it by throwing a bone it has ripped from its own skeleton. Then, despite a narrow escape in the wildlife exhibits, Larry manages to lock up the lions. Finally, he double-checks his belt, only to discover that a capuchin monkey named Dexter has in fact stolen his keys. When Dexter destroys the old guards' instruction manual, Larry is forced into humiliating himself.
Eventually Larry is rescued from an odd feud between miniatures, pitting a Wild West buckaroo named Jedediah against a Roman General named Octavius, by a wax model of Theodore Roosevelt ,who later explains that ever since an Egyptian artifact — the Tablet of Akmenrah — was brought to the museum in 1952, everything comes to life each night. However, if the exhibits are outside of the museum by sunrise, they literally turn to dust. Roosevelt proceeds to help Larry by restoring order, but insists that it will be the last time he shall ever do so.
While initially unnerved, Larry decides to remain as a guard. On Cecil's advice, Larry begins to study the history of the events and people in the exhibits to prepare himself better for their animation. He meets Rebecca Hutman who is writing a dissertation on the life and times of Sacagawea, and learns much of the history of the various exhibits from her.
The next night, Larry uses what he has learned to better control the exhibits, but this, his second attempt, fails when one of the four Neanderthals sets fire to his compatriots' display, which Larry is forced to extinguish using a nearby fire extinguisher, while the Neanderthal escapes out a window, only to be transformed into dust when the sun rises. Larry barely manages to keep his job after the Museum's director, Dr. McPhee, discovers the mess. Larry tries to tell Rebecca about what happens every night, even offering to let her meet Sacagawea to help with her dissertation, but Rebecca does not believe him.
Two nights later, Larry brings Nick to the Museum, but fails to impress him when nothing comes to life. Just as Larry convinces Nick to wait for the promised event, they find Cecil, Gus, and Reginald stealing the Tablet of Akmenrah. Cecil then reveals the truth to Larry: that like the museum exhibits, the guards receive vital emanation from the Tablet. Now accustomed to this vigor, they are unwilling to forsake it and accordingly intend to steal the Tablet, along with various other Museum artifacts to fund their retirement, and thus frame Larry for the theft. Nick, after prompting from Larry, reactivates the Tablet's power and brings the exhibits to life once more. Cecil then grabs the Tablet back and locks Nick and Larry in the Egyptian room.
Larry calls for Theodore Roosevelt for help, but Roosevelt insists that Larry solve this problem on his own. The only thing left for Larry to do is release the mummy of Pharaoh Akmenrah himself, the owner of the tablet. Surprisingly Akmenrah speaks English; when asked to explain this, the Pharaoh informs Nick and Larry that he had spent many years as an exhibit in the Egyptology Department at Cambridge University. After Larry introduces himself and Nick, Akmenrah then asks them to bestow his Tablet upon him, so he can "claim his kingdom". Larry informs Ahkmenrah that the Tablet has been stolen, convincing the Pharaoh to free them. The three new friends then set out to reclaim the Tablet.
Larry discovers that the other exhibits are fighting with each other; having attracted their attention with the intervention of an animated Moa, he rallies them around the common cause of saving their own ability to be animated and thus acquires their help in retrieving the Tablet. Though the exhibits manage to capture Gus and Reginald without difficulty, Cecil escapes with the Tablet by stagecoach, whereupon Larry, Nick, Akmenrah, Jed, Octavius, and Attila the Hun pursue him through Central Park, eventually capturing him thanks to Larry's quick thinking of halting the horses with a secret word, "Dakota."
Because the exhibits who have come outside may be destroyed by sunrise, Larry gives the Tablet to Akmenrah, who immediately uses its power to return all the exhibits to the museum. Rebecca, in a taxicab, sees the exhibits crossing the road in front of her and realizes that Larry was telling the truth. Entering the museum, she is introduced by Larry to Sacagawea.
The next day, Dr. McPhee fires Larry despite his effort to clean up the museum; but when the reports issued by the news media begin increasing the Museum's popularity, he readmits Larry. Some time later, Larry appears in Nick's classroom during Career Day. Later that night, Larry returns with Nick and all the exhibits celebrate. Cecil, Gus, and Reginald eventually become janitors at the Museum; a stereotypical punishment in comedy films for defeated antagonists (and still allows them to be around the energies of the tablet).

Taken from Wikipedia