In
1938, in Egypt a team of archaeologists are digging into a tomb to look for a
valuable artifact. A young boy falls through a hole that leads his father and
the others to what they came for - the tablet of Ahkmenrah. Several local men
see the tablet and say that if the archaeologists remove it, then "the end
will come".
In the
present day in New York City, Larry Daley is overseeing a nighttime event at
the Museum of Natural History with Dr. McPhee in attendance. Larry gathers the
favorite exhibits, including Theodore Roosevelt, Attila the Hun, Sacagawea,
Dexter the Capuchin Monkey, and Rexy the Tyrannosaurus skeleton. Elsewhere,
Jedediah and Octavius are watching a cat video on YouTube.
Larry
meets a new wax figure Neanderthal named La who was modeled to look like Larry
as a joke. Ahkmenrah had earlier alerted Larry to the fact that the tablet is
starting to corrode, causing all the exhibits to act abnormally. The corrosion
causes chaos during the event, with the attendees having to flee from dangers
caused by the affected exhibits. When Larry returns home, he catches his son
Nicky throwing a party for which he is serving as the DJ. Nicky tells Larry
that he does not intend to apply to college, wanting to take time to pursue
being a DJ and to figure out what he wants to do with his life.
Larry
researches the tablet and learns that Cecil Fredericks, the former museum
security guard that tried to steal the tablet for himself, was the boy present
at the discovery of the tablet. Larry finds Cecil in a retirement home along
with his cohorts Gus and Reginald. Larry explains to Cecil what is happening
and he recalls "the end will come" prophecy, realizing it was not an "end
of the world" prophecy but a reference to an end to the magic. He suggests
that they consult Ahkmenrah's parents, who are in the British Museum. Larry
later goes to Dr. McPhee, who is in the process of being fired, and convinces
him to call the British Museum and allow Larry to travel there with Ahkmenrah
and the tablet.
Larry
and Nicky travel to London to get to the British Museum. They meet the security
guard of that museum, Tilly, who lets them through the gate. When Larry gets
into the museum, he sees that Laa, Teddy, Sacagawea, Attila, Dexter, Jed, and
Octavius have all stowed away to join on the adventure. The Tablet brings the
British exhibits to life and the gang encounters a Triceratops skeleton which
chases them. They are saved by Sir Lancelot. Unfortunately, the gang has lost
Jed and Octavius; they discover that they have fallen into the ventilation
chambers. Larry sends Dexter into the ventilation with Nicky's cell phone
attached to his waist to find Jed and Octavius. Jed and Octavius land on a
Pompeii exhibit just before it erupts. The gang fights off a nine-headed
Xiangliu statue, which Larry defeats using a defibrillator. Meanwhile, Dexter
urinates on the lava to save Jed and Octavius.
The
gang finds the tombs of Ahkmenrah's parents, Merenkahre and Shepseheret.
Merenkahre is at first hesitant to reveal the truth behind the Tablet, but he
eventually admits that it was a gift made for his son when he was a baby to
keep the family together always. Endowed with the power of Khonsu, the tablet
needs moonlight to retain its magic.
Lancelot
steals the tablet, thinking it to be the Holy Grail and then leaves to find
Guinevere. The tablet continues to corrode, causing Teddy's hands to return to
wax and Ahkmenrah to age. The gang splits up to find Lancelot and regain the
tablet, but Larry is caught by Tilly, who then locks Larry and Laa in the
security room. There, Larry starts to think about his relationship with Nicky.
Laa eventually smashes the glass of the door with his head to free Larry and
himself. Larry and the gang continue to search for Lancelot again, but are
cornered by the Trafalgar Square lion statues. Larry distracts them with a
flashlight like in the cat video Jed and Octavius had previously watched on
YouTube.
Lancelot
has made his way to a local theater showing a Camelot production starring Hugh
Jackman as King Arthur and Alice Eve as Guinevere. Sir Lancelot runs onstage
with the tablet and tries to convince "Guinevere" to join him. The
actors eventually convince Lancelot that they are actors, upsetting Lancelot
and causing him to take a lighted torch from the stage and run to the roof.
Larry and the gang chase Lancelot and attempt to get him to adjust the tablet
appropriately in order for the moonlight to restore it. Larry convinces
Lancelot to give him back the tablet to save his friends once the other
exhibits all return to their lifeless state due to the corrosion of the tablet.
Larry then adjusts the tablet and it is restored by the moon, reanimating
Teddy, Dexter, and the rest.
Larry
returns the tablet to Merenkahre after the New York exhibits explain that they
believe the tablet and the pharaohs should stay together. On the way out, Larry
catches Tilly and Laa in a romantic moment. As they leave, Larry tells Tilly
that, starting the next day, she will have the greatest job in the world. Back
in New York, the exhibits accept their fate and say goodbye to Larry.
Three
years later, a British Museum treasures exhibition event is happening at the
American Museum of Natural History. Tilly shows up to McPhee's office with a
box. McPhee explains that Larry left the museum and went on to become a
teacher, after taking the blame for what happened when the exhibits went
ballistic, granting McPhee his job back. Tilly opens the box and takes out the
tablet. She brings Dr. McPhee to show him all the exhibits coming to life,
including some new light displays. The exhibits then have a party.
Outside,
Larry pauses on the sidewalk to see the flashing lights from inside the museum;
as he watches, he smiles