The year's best martial-arts action so far can be found in District B13, an otherwise flimsy sci-fi thriller from the Luc Besson workshop. Publicity materials claim that the film showcases Parkour, a French form of martial arts that concentrates on movement-jumping, running, climbing, etc.-rather than fighting. But District B13 works best as a throwback to the heyday of Hong Kong action films. Jaw-dropping stunts alternate with stiff acting and brain-dead plotting, the hallmarks of the guilty-pleasure genre.

By the year 2010, the slums of Paris have been walled off from the rest of the city, leaving gangsters like Taha (Bibi Naceri, who also co-wrote the screenplay) in charge. Trying to keep his apartment building drug-free, Leïto (David Belle) captures Taha and hands him over to the police, only to be arrested and jailed in a double-cross. What's worse, his sister Lola (Dany Verissimo) ends up in Taha's clutches.

Undercover cop Damien (Cyril Raffaelli) single-handedly dismantles a casino filled with 35 gun-toting crooks before receiving his next assignment. Government officials have lost an advanced "clean" nuclear bomb that can kill people while leaving buildings unharmed. Krüger (François Chattot) orders Damien to go into District B13 to retrieve it, and assigns Leïto as his partner.

Antagonistic at first, the two realize they must work together when they learn that Taha has the bomb. They confront the gangster in his headquarters, where they find out that he has started the detonation sequence. When Krüger refuses to pay the crooks a ransom, it's up to Damien and Leïto to defeat Taha, rescue Lola and defuse the bomb.

Shot primarily in Romania, District B13 sports a grungy, decayed look of abandoned factories and Iron Curtain-era apartment blocks. Director Pierre Morel, a cinematographer on Besson projects like Unleashed and the first Transporter, speeds the film along with verve, relying on quick cuts and a pounding hip-hop score to distract viewers from the threadbare script. Apart from the amusing Naceri and the beefy Tony D'Amario, playing a thug with his name carved into his haircut, the acting here is rudimentary. Of the two leads, both former stuntmen, Belle seems slightly more accomplished than Raffaelli, who at times resembles a slack-jawed Chris Elliott.

Few will be coming to District B13 for the acting, of course. Like many of the incredibly prolific Luc Besson's productions, the film is a streamlined machine for delivering action. Raffaelli sticks to the traditional: guns, punches and kicks. He's effective despite an annoying hitch in his movements. Belle doesn't fight so much as fly, jumping through windows and off buildings with reckless élan. He is the best reason to see District B13, an imperfect but still diverting bit of hokum.

-Daniel Eagan