In "Constantine," Keanu Reeves plays a kind of INS agent on the border between this mortal coil and the eternal hereafter. Part detective, part border cop, part exorcist, John Constantine (no relation to the emperor who secured the power of the Christian church in the Roman Empire) spends his days extracting demons from little girls and making quick jaunts to hell.

According to the movie's dogma, heaven, hell and Earth coexist on parallel planes, so crossing over takes a fraction of the time it would take to cross town at rush hour. All Constantine has to do is kill himself for a second and he'll wake up in exactly the same room, on the same street corner or on the same devilish stretch of the 101 Freeway where he was standing at the time — except the atmosphere will be on fire, and demons with hollow skull cavities will be darting around ripping new arrivals to pieces. Heaven, meanwhile, we learn toward the end of the movie, looks exactly like downtown on a weekend morning after a good rain, which struck me as a missed opportunity. Why not Malibu full of brainy angels greenlighting good movies?

Not that "Constantine," based on D.C. Comics' "Hellblazer," doesn't have more than its share of gloomy pleasures, especially for fans of Dan Brown and the occult. For one thing, it's loaded with more cool Christian iconography than a souvenir stand at Lourdes. And Keanu Reeves has no peer when it comes to playing these sort of messianic roles — he infuses them with a Zen blankness and serenity that somehow gets him through even the unlikeliest scenes with a quiet, unassuming dignity. Another actor might panic and resort to bombast in an attempt to detract attention from glaring holes in the logic; he might start running around yelling things like "Where is she?!" in a demanding tone of voice. Not Reeves, though. He lets the illogic flow through him without resisting it. He is the illogic.

A psychic brooder with an eye for spotting illegal hellions roaming the worldly plane, Constantine is one of the few humans hip to the U.S.-Soviet style détente between the blithe superpowers God and Satan, who have agreed not to have direct contact with the secular world but to stock it with half-human, half-angel/demon "influence-peddlers" instead. Now in the final stages of lung cancer and barred from heaven because of a teen suicide attempt, Constantine is working overtime to change the admissions policy, but the archangel Gabriel (Tilda Swinton) won't budge. Lately, though, he's noticed hell has been breaking loose its inmates, and he's eager enough to get on God's good side to look into it, especially after detective Angela Dodson (Rachel Weisz) — a tough-but-sexy loner cop in a tank top, whose twin just performed an assisted swan dive off the roof of the psych ward — insists. Then they're off to save the world.

Weisz doesn't share Reeve's gift for affectless heroism — not that the deadly intensity of her character is entirely her fault. Saddled with the unfortunate burden of playing the 21st century damsel in distress (you know the type — tough, single, lives alone, carries a gun) she spends half the movie trying to look poker faced in a wet white tank top. Aside from Angela, Constantine has assembled a nice psychic friends' network for himself. There's Hennessy (Pruitt Taylor Vince), the psychic, alcoholic priest with the lazy eye; Midnite (Djimon Hounsou), former demon hunter turned club owner; and acolyte, Chaz (Shia LaBeouf), who's not psychic but who reads up on all the latest trends in Catholic arcana and "Da Vinci Code"-style doctrinal conspiracy theories.

The first scenes are spare and powerful. In one, a poor Mexican laborer discovers a dagger wrapped in a Nazi flag under a ruined Church. The dagger is the Spear of Destiny, which the movie suggests is the weapon that killed Jesus. It's also the weapon that turns the laborer into an indestructible force of evil, possibly the son of the devil, because instantly he's surviving a horrific accident, stealing a car and entering California illegally. In another, a shameless homage to "The Exorcist," a nice-looking Christian lady in L.A.'s Chinatown makes herself a pot of tea while in the next room her preadolescent daughter scuttles around the walls like a soft-shelled crab until Constantine arrives to give her the Linda Blair treatment.

But the movie gets bogged down around the time that Constantine and Angela start developing feelings for each other and she starts getting soaked with alarming frequency.

It will shock nobody to learn that director Francis Lawrence previously enjoyed a career directing music videos, especially once the special effects and music video tropes threaten to take over. If there's one thing the world never needs to see again, it's an underground nightclub scene where the hipster damned go to see and be seen. Not that anyone expects one's occult thriller to be anything less than Byzantine, but despite some witty special effects and a appealing concept, "Constantine" meanders in too many directions to make much sense even to itself. The "demonic images" that earned its R rating consist of a porridge of mixed metaphors.

Balthazar (Gavin Rossdale), a sort of half-demon lobbyist from hell, dresses like a stockbroker and hangs out in a conference room where he plays what could be a karaoke video for a John Ashcroft song — soaring eagles and rippling flags in an endless loop. As Satan, Peter Stormare dresses up like John Travolta circa 1977 and plays the part for giggles. By the time it's revealed that the sudden influx of hell nationals into the world was facilitated by a very big cheese in celestial circles, one half expects Michael Medved and Rush Limbaugh to crash through the theater ceiling brandishing swords.

In the mock-solemn, patently silly universe of "Constantine," it wouldn't look a bit out of place.