By John Mulderig | Catholic News Service

NEW YORK  -- Despite its ponderous title, "Valerian and the City of a Thousand Planets" (STX) turns out to be a flashy but lightweight sci-fi adventure likely to divert those grown viewers content to munch their popcorn and enjoy a break from the heat of summer.

Moviegoers seeking something more memorable, by contrast, will be disappointed. And some gritty elements incorporated into the film suggest that even most mature teens should skip this trip to the stars and instead stay safely earthbound.

It's the 28th century, and devil-may-care intergalactic law enforcement agent Maj. Valerian (Dane DeHaan) finds himself sharing both romantic tension and a series of crime-busting exploits with his more serious-minded partner, Sgt. Laureline (Cara Delevingne). Initially, the latter involve the legacy of the destroyed planet Mul.

Small reptiles from that lost orb, known as Mul Converters, had the power to multiple pearl-like gems that doubled as energy-producing wonder minerals. Now, the last remaining Mul Converter has fallen into the wrong hands, and Valerian and Laureline's boss, the Minister of Defense (musician Herbie Hancock), dispatches them to retrieve it.

Later phases of the plot concern the fate of Alpha, the titular metropolis. This mega-space station, a gathering place for a wide variety of life forms, is under threat from an unidentified force, and it's up to our heroes to get to the bottom of the mystery.

In adapting a series of graphic novels by Pierre Christin and Jean-Claude Mezieres, writer-director Luc Besson excels at such sequences as an interdimensional chase through an exotic bazaar. Yet his sometimes baroquely overwrought film is longer on style than ultimate impact.

The love story sees playboy Valerian -- whose promiscuous past is treated lightheartedly -- anxious to mend his ways in favor of marital commitment. And there are incidental religious references in the dialogue, though these are partly offset by equally fleeting lines with a pagan ring to them.

In addition to an early scene in which the main duo canoodle, Valerian's detour through Alpha's gritty red-light district -- during which he's momentarily mesmerized by shape-shifting stripper-prostitute Bubble (pop star Rihanna), and also has to deal with her crafty pimp, Jolly (Ethan Hawke) -- puts the proceedings well out of bounds for youngsters.

Bubble remains at least minimally clad. But some of her ever-changing costumes play on fetishistic fantasies, making this portion of the otherwise mostly inoffensive "Valerian" unsavory even for older viewers.

The film contains gunplay and other stylized violence, a prostitution theme, scenes of sensuality with partial nudity, a mild oath and a couple of uses each of crude and crass language. The Catholic News Service classification is A-III -- adults. The Motion Picture Association of America rating is PG-13 -- parents strongly cautioned. Some material may be inappropriate for children under 13.

Mulderig is on the staff of Catholic News Service.