“THE LEGO NINJAGO MOVIE”

** 1/2

(PG, 1:41)

If you’re of a certain age and childless, it’s entirely possible you haven’t the foggiest idea what a “Ninjago” — of the latest Lego movie — might be. Apparently it is both a show and a toy, but that’s as far as I got into the Wikipedia article. With the wild success of both “The Lego Movie” and “The Lego Batman Movie” released just earlier this year, it stands to reason that Warner Bros. would strike while the iron is hot and churn out more Lego-themed movies, like “The Lego Ninjago Movie,” which sadly proves that when it comes to the superfun Lego movies, there can be diminishing returns.

The genius of “The Lego Movie” and “The Lego Batman Movie” lies in the extremely high joke density of those films, which are thick with verbal and visual gags, nearly overwhelming in their detailed specificity to both the Lego character style, and the incredibly rich worlds and mythology created around these little plastic toys. “Ninjago,” directed by Charlie Bean, Paul Fisher and Bob Logan, and credited to no less than nine screenwriters (including Fisher and Logan), doesn’t quite maintain that level of mania that make both “Movie” and “Batman” deliriously fun.

Signaled by the vintage WB logo at the beginning, and a live-action opening featuring Jackie Chan as a kindly shop owner telling the story of Lloyd and Ninjago to a young patron, “The Lego Ninjago Movie” is inspired by 1970s kung fu and monster movies. The young hero, Lloyd (Dave Franco), is a forlorn teenager in the seaside city of Ninjago, leading a secret double life as both the much-maligned son of evil villain Garmadon (Justin Theroux) and the Green Ninja of the ninja crew that saves the city from Garmadon’s destruction. Think of the ninja crew like the Power Rangers: These teens have different colors, different powers, and ride around in giant animal-shaped robots fighting Garmadon and his army.

Lloyd’s just a sensitive kid with daddy issues, and therefore, he overcompensates a bit. During a battle he accidentally unleashes a terrifying monster — a furry feline creature named Meow-thra (a live house cat, batting around Ninjago like a ball of yarn). With his posse of ninja buddies, under the guidance of their sensei, Mr. Liu (Chan), Lloyd sets out on an adventure to retrieve a superspecial weapon to stop Meow-thra. There’s just one wrinkle: His overbearing blowhard of an evil dad joins them on the trip.

“Lego Ninjago” maintains the silly and irreverent tone of the prior films, and the other ninjas are voiced with great personality by comic stars Kumail Nanjiani, Abbi Jacobson, Zach Woods, Fred Armisen and Michael Pena.

What doesn’t quite work is the emotional story between Lloyd and Garmadon as they get to know and accept each other, which is the heart of this tale. If the story of your film requires a lot of emotional expression, it might not work best with characters that have flat round plastic heads and painted-on features.

Some aspects of the film are quite entertaining. Garmadon is a great character, especially as voiced by Theroux (his pronunciation of Lloyd as “Luh-Loyd” doesn’t get old). It’s a light, serviceable romp around the Legos but doesn’t come close to the high-key antics of the first two films in the series.