Starring Ben Stiller and Robin Williams. Rated PG. Now playing

For the first part of Night at the Museum’s swan song, you can’t help but feel the franchise should be boxed up and put back into storage. The initial novelty of historical figures come to life waned long ago. How many times can you watch Teddy Roosevelt or Genghis Khan start walking and talking again? But the third and final installment improves hugely when it gets its London calling—and I’m not referring to the Clash song, though it is played here, with unintentional irony, over pretty skyline shots of the U.K. capital.

The British Museum offers not only rooms full of Greek statues, taxidermied animal heads, dinosaur bones, armour-clad wax knights, and mazelike Escher paintings to come to life, but a crew of charismatically funny new characters—namely Rebel Wilson as a beyond-clueless security guard who wields a hammer for protection, Dan Stevens as a laughably chivalrous Lancelot, and Ben Kingsley as a kohl-eyed pharaoh.

Ben Stiller’s Larry, once a security guard and now a director of the American Museum of Natural History, has brought his crew to London to find Kingsley’s Merenkahre (who’s displayed there). He’s the only one who will know why the magic Egyptian tablet that brings the museum exhibits to life is losing its powers.

The plot is little more than an excuse to unleash special effects, which this movie does far better than its predecessors. Diorama-size cowboy Jed (Owen Wilson) and Roman Octavius (Steve Coogan) get into spectacular trouble in a Pompeii exhibit and the entire gang has to take on a gargantuan, multiheaded serpent in the Asian wing.

It’s all mindless entertainment, of course, but there are at least a few laughs along the way, including Wilson’s flirtations with the Neanderthal Laaa (also played by a brow-enhanced Stiller) and Merenkahre’s quick history lesson on the Exodus. And then there’s Lancelot crashing a London stage version of Camelot, insisting on calling its star, Hugh Jackman, “Huge Act-Man”.

As for the late Robin Williams, who plays Roosevelt? His final movie role is not a big one, but he has a surprisingly prescient goodbye with Larry. And that’s about as close to poignancy as you get in this loony but not totally unlikable last act.