Deep in the forest, by a rippling creek, ringed by the song of birds and the soft crush of animals moving across pine needles and moss, the Cash family reside.

It's an idyllic life, but a rigorous one: The father, Ben (Viggo Mortensen), rules over his six kids, testing them on the books they've read (Middlemarch, The Brothers Karamazov, Karl Marx, Noam Chomsky), leading them on rock climbs and long runs, training them to use a knife to kill and skin deer. Ben teaches his sons and daughters hand-to-hand combat, too - how to use a long, serrated blade on another human.

OK, maybe a little extreme.

But that's the way things are as Matt Ross' odd and wonderful Captain Fantastic begins. Ben's an old hippie, a radical. He has taken himself off the grid - and taken his brood with him. His wife, Leslie, has been away for months - it's not immediately clear why. It becomes clear, though. And her absence eventually forces Ben and his children to climb into their old school bus, with its book shelves and bunks, and leave their rustic compound in the Pacific Northwest for the "real world."

For the children - Bodevan (George McKay), who would be finishing high school if he weren't enrolled in this unique homeschool; the teenage girls Kielyr (Samantha Isler) and Vespyr (Annalise Basso); the middle son Rellian (Nicholas Hamilton); the little Zaja (Shree Crooks) and Nai (Charlie Shotwell) - the experience is jolting.

Ross, an actor directing only his second feature (he's Gavin Belson in the HBO series Silicon Valley), has crafted a script that offers a perceptive, piercing, often funny look at what exactly family values are. Captain Fantastic (not sure about that title) follows the Cashes as they head for New Mexico, realizing along the way that perhaps this alternative lifestyle is too alternative.

The kids' maternal grandparents (Frank Langella and Ann Dowd) appear determined to wrest them away; meanwhile, Ben, in full command back in the forest, begins to doubt himself. Deep-seated beliefs are shaken.

"You made us freaks!" the boy Rellian accuses Ben, and he has a point.

Captain Fantastic, then, is a story about culture shock - and the shock waves that threaten to break up a close-knit, loving clan. Mortensen, who has played a Navy SEAL instructor (G.I. Jane), a Woodstock-era itinerant clothing merchant (A Walk on the Moon), a lethal Russian mobster (Eastern Promises), and a mysterious Middle Earth ranger (a little trilogy called The Lord of the Rings), is just about perfect here.

One minute he's exclaiming "Stick it to the man!" - delighting his kids as they outsmart cops and supermarket managers. The next, he's strumming a guitar in a campfire jam. Or facing off against his angry, affluent father-in-law. Or stopping to consider that his strident child-rearing philosophy might have been a mistake.

But if this is Mortensen's movie, he shares it with an amazingly adept group of young actors. From McKay (conveying a keen intellect and an aching shyness) on down to the tiny Shotwell, Ross' ensemble of pip-squeaks, preteens, and adolescents works in sync, and in competition with each other, just like real siblings. How Ross cast this gang, and how he got these very different kids to coalesce, well, it's a feat.

Captain Fantastic takes a couple of shortcuts, story-wise, emotionally, that threaten to compromise a work of fierce intelligence and integrity. But it's a rare movie that asks such big questions - about parenting, about family, about modern-day America - and comes up with answers that are moving and meaningful, that make you laugh and cry.

So, let's give the movie a break. Mortensen, Ross, and company have earned it.

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@Steven_Rea

MOVIE REVIEW

Captain Fantastic

***1/2 (Out of four stars)

yDirected by Matt Ross. With Viggo Mortensen, Frank Langella, George McKay, Nicholas Hamilton, and Annalise Basso. Distributed by Bleecker Street.

yRunning time: 1 hour, 58 mins.

yParent's guide: R (nudity, profanity, adult themes).

yPlaying at: Ritz East

and Carmike Ritz Center/NJ.EndText