Mia is a trapped and angry teen growing up in a trashy apartment complex in Essex, on the marshy eastern reaches of the Thames River. It's not all that far from London, really, but it's cultures away. She and her little sister live with their boozy mom, an aging party girl who's still trying to make miniskirts work for her. Mia's daily life is defined by concrete and litter, cramped rooms and cheap scuffed linoleum. There might as well be a billboard out in the scrubby parking lot announcing: "No Future."

Katie Jarvis, who plays the 15-year-old Mia, was discovered in a provincial train station after having an argument with her boyfriend. She's never acted before, but she carries every scene in "Fish Tank" with startling confidence; and with director Andrea Arnold calling the shots, she's in the best of hands.

The movie is about youthful frustration and the ways in which grownups betray kids; it's also about the way in which kids can come to accept those betrayals as just another bum card in the dismal hand that life has dealt them. Mia has never had a boyfriend, but her mother (Kierston Wareing) always likes to have a man around. The latest is Connor (Michael Fassbender, the English officer in "Inglourious Basterds"). Connor is a wiry, cheerful security guard in his early thirties who sleeps over with mom on a regular basis. He's sweet to the two girls, and Mia starts to see him as a stabilizing, dad-like presence; she likes him. Already we can feel betrayal beginning to grow in the shadows of the story.

Mia doesn't get along with the other girls in the complex -- she doesn't get along with anybody, really -- and she's prone to head-butt the ones who give her any guff. Like them, though, she's obsessed with working up the sort of dance routines she's seen in hip-hop music videos; and in one of the movie's several quietly beautiful scenes, we see her in an empty room dancing alone to music only she can hear in her headphones, while twilight gathers outside the windows.

After Mia sees a poster advertising auditions for young dancers, Connor encourages her to give it a shot. He also offers her a slug of vodka from a bottle he's rarely without. We slowly begin to see where this is going, but the director is in no hurry to get there. With its unemphatic hand-held camerawork, the movie feels artless and unmediated; it puts us among the characters and simply bears silent witness as their lives play out.

Arnold captures Mia's growing affection for Connor in surprising flashes: a quick shot of her hand as she grasps his shoulder to steady herself while he ties her shoe; a close-up of her intoxicated face as she inhales the scent of his cologne. And in the picture's most startlingly original scene, the director vividly captures the girl's muddled relationship with her mother: The two of them have exchanged harsh words, but then they both succumb to a song drifting out of the stereo, and begin to sway to the music. It's one of those rare movie interludes that you feel certain you've never seen before.

Arnold, who won an Oscar for her 2003 short, "Wasp," has a forthright style that can shade into rapture, and her presence is never apparent in the scenes she creates. She takes the story in unexpected directions that seem inevitable only in retrospect; and in the process, she turns Jarvis into a star. The picture offers hope at the end, but it's qualified. Can Mia escape her stifling life? And even if she can, how far can she really run?

Don't miss Kurt Loder's review of [article id="1629740"]"The Book of Eli,"[/article]also in theaters this week.

Check out everything we've got on "Fish Tank."

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