Walk the Line review – Johnny Cash biopic that taps into the music’s driving force

There's a warm and generous richness to this biopic of country singing legend Johnny Cash; you'd need a heart of stone not to love it, and toes of stone not to tap along to the music's driving force. Director and co-writer James Mangold tells a seductive story packed with loving period detail of Cash's grim boyhood picking cotton in Depression-era Arkansas, his excruciating guilt at the death of a brother, unhappy military career, too-early marriage and children, all before that deep groan of a singing voice found ecstatic expression as that of the "Man in Black", discovered by Sam Phillips in the Sun Studios in Memphis, Tennessee.

He became the existential outlaw who shot a man in Reno, just to watch him die - and maybe nothing in the rest of his career matched the brilliance of that one line. But Cash's instinctive tendency to side with the poor and the dispossessed made him the hero of prison inmates all over the US, despite having had himself only a handful of overnight stays in prison. (The movie, with some narrative sleight-of-hand, also appears to suggest a little trouble with the military authorities.) To tell his story, Mangold flashes back from Cash's finest hour: his live gig at Folsom Prison, California in 1968, which as a popular music event here looks like a shot of neat whiskey to the gallon of Diet Coke that was Live8.

The plot has the same Horatio Alger-ish trajectory as the recent film about Ray Charles, starring Jamie Foxx. That didn't have anything to match the equal-status love affair of Cash and country singer June Carter, though. The lovers are here played by Joaquin Phoenix and Reese Witherspoon, who also do a very impressive job of singing all the songs.

And it is actually Witherspoon's film. With a sweet-natured intelligence and the kind of humility that upstages all the male alpha-egos, Witherspoon turns June Carter into a superbly watchable character. She's the sassy gal who makes up for what she thinks of as a second-rate singing voice with a gift for snappy comedy at the microphone, enduring the sour testosterone on the tour bus, with Elvis Presley and Jerry Lee Lewis. No one who saw Witherspoon in Alexander Payne's Election could doubt her outstanding talent - which went behind a cloud for those lucrative but moderate Legally Blonde movies - and it has come to full, unironic flower here. Witherspoon has one of the most extraordinary faces in the cinema, with an effortless mile-wide grin to match and eclipse Julia Roberts or Hillary Clinton. Her shovel-sharp chin and candid eyes are positioned in a face that is almost hyperreal in its clarity and intensity. It is as eloquently drawn as a cartoon.

One moment really stands out. June is accosted by a middle-aged woman in the Bible Belt. Believing this person to be a fan, June turns on the full beam of her southern politeness and charm. But the woman merely snarls that June's recent divorce was an abomination. June replies humbly: "I'm sorry I let you down, ma'am." Her face turns pale and the corners of her mouth turn down - but she snaps back into cheerfulness a minute later. Her contrition is genuine, but so is her innate self-belief. Another sort of movie might have required this woman to be bested and humiliated in some retaliatory scene, but the incident is merely left alone (though the woman's glowering face appears in the audience later) as testament to June's essential grit. It demonstrates something similar in Witherspoon, too. And it is her face, that radiant moon of a face, which shines out.

Phoenix is fractionally less impressive, though still very good. He wields his acoustic guitar not like a gun but like a badge or a shield, hoiking it up across his chest like a boy with a grownup instrument too big for him: a strange, but distinctive and oddly affecting gesture. Phoenix's best moment is when he and his boys audition for Phillips with a dull gospel number; Phillips curtly silences Cash, and challenges him to imagine being hit by an automobile and sing the song he'd want to be remembered for. Right there is where Cash's dark, melancholy, passionate voice is born.

Joaquin Phoenix would deserve an Oscar, if he got one; but my vote, and my hope, is to see fellow nominee Witherspoon get up on stage to give a twangy speech. Or at the very least sing one of the songs.