Danny Boyle's "Slumdog Millionaire" is a head-first immersion into the roiling urban culture of modern India, a quest movie that follows its teenage hero through the slums of Mumbai into slave camps, gangster dens and garish bordellos on his way to unexpected fame, unimaginable fortune and — he hopes — a reunion with the long-lost love of his young life. It's a unique adventure movie, and it leaves you breathless.

Boyle is a director who never seems to make the same sort of film twice. He's previously ventured into snarling drug comedies ("Trainspotting"), tropical island fantasies ("The Beach"), zombie horrors ("28 Days Later") and visionary sci-fi ("Sunshine"). Now he brings his rousing genre sensibility to bear on a vibrant world that's new to most of us, and we feel that we're discovering it, in considerable wonder, right along with him. (Boyle also credits Mumbai-based casting director Loveleen Tandan as the picture's co-director.)

We first meet Jamal Malik (English TV actor Dev Patel, scoring memorably in his first film role) as an 18-year-old "slumdog" — an unlikely street kid who's become a star contestant on the Indian version of "Who Wants to Be a Millionaire." Jamal's vast store of oddball knowledge has ticked off the show's slick, preening host, Prem (Bollywood veteran Anil Kapoor), who's convinced that this lowly urchin must somehow be cheating. When Jamal arrives at the brink of claiming the show's top prize of 20 million rupees (more than $400,000), Prem calls in the police, who drag the boy off to headquarters to sweat the truth out of him.

The movie's structure is keyed to Jamal's answers to various questions on the show. As he explains to the cops — between kicks and punches — how he came to know such things as the name of the actor who starred in a decades-old movie, the statesman pictured on the U.S. $100 bill and the American gunsmith who invented the revolver, we flash back to various points in Jamal's life — to the murder of his mother and his battles (both desperate and hilarious) to survive on the city's swarming streets with his tough older brother, Salim (played as a young man by Madhur Mittal), and their fellow orphan, pretty little Latika (played as a grownup by Indian model Freida Pinto). Each of these flashbacks is a setpiece sequence, often of startling invention. We see that the younger Jamal actually met the old actor one day after falling through the opening in an outhouse toilet and running up to him on the street, covered in disgusting muck, to get his autograph. We also see how he came into possession of a $100 bill while hustling tourists at the Taj Mahal (the movie's only pulled-off-a-postcard interlude, but a funny one). The Colt revolver comes into play after Jamal and Salim escape from a hideous "orphanage" where children are taught (and maimed) to be beggars — a place where they had to leave Latika behind. "What happened to her?" Jamal's police interrogator asks. "It took me a long time to find out," he says.

When he does find Latika, it's in the most distressing circumstances. Then he loses her again. He's competing on Prem's popular game show, it turns out, not just for money, but in the hope of getting Latika's attention, wherever she may be, and of somehow getting her back.

"Slumdog Millionaire" is an affectionate approximation of Bollywood romance, but without the stylized sheen. Boyle and his cinematographer, Anthony Dod Mantle, have devised a very Western action style for the film — they thrust us into the middle of each adventure, but always pull back to catch the teeming context — and the propulsive score, by Bollywood soundtrack auteur A. R. Rahman, is hip-hop fusion of a very up-to-date kind. The girl of Jamal's dreams is classically beautiful, in the Bollywood way, but he himself, with his dark, slouchy reticence, is a far cry from the pearly toothed young gods who usually feature in such pictures. The movie happily promotes the possibility that love can conquer all (very Bollywood, and Hollywood, too, of course). But as Jamal discovers, over and over again, in the most remarkable ways, it's never easy.

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