Love him or hate him, Johnny Cash was one of the towering figures in country music. Walk the Line is as good an explanation as you will find about his role as a musician and star. By showing his flaws as well as his strengths, the film becomes a stirring example of a peculiarly American success story, as well as a vivid reminder of the price of fame. Outstanding performances by Joaquin Phoenix and Reese Witherspoon help make it the strongest country-music film in years.

The story follows a familiar but comfortable formula, filling in Cash's humble beginnings in Dyess, Arkansas; his conflicted relationship with his demanding father, Roy (a steely Robert Patrick); and his early failures as a husband, father and singer. Screenwriters Gill Dennis and James Mangold (who also directed) throw in hints about the sources of Cash's inspiration-at first movies and other pop songs-but focus squarely on the musician's thirst for success. In Memphis, Sun Records founder Sam Phillips (Dallas Roberts) helps Cash define the raw, propulsive sound that becomes his trademark. An audition for "Folsom Prison Blues" shows the two men molding Cash's outsized persona into something America could accept.

But Cash couldn't lose his maniacal intensity. Grinding tours with Elvis Presley (Tyler Hilton) and Jerry Lee Lewis (Waylon Malloy Payne) get him addicted to amphetamines, but also introduce him to June Carter (Reese Witherspoon). Once his childhood idol, and an offspring of country music's most famous family, June has settled into a niche as a cornpone comedienne. She treats Cash warily, keeping him at arm's length as he clumsily tries to woo her. They fall in love through music, but life and its problems keep them apart.

Mangold shoots their duets in thrilling close-ups that make their affair seem inevitable. The music throughout has a tangible excitement that's often missing from movies, but Mangold is fortunate to be working with some of the strongest songs in country. The understated production design ranges expertly from rural cotton fields to Las Vegas, and the film takes the time to get the supporting characters, in particular the musicians, right. Judging from his scenes here, it's easy to see why everyone was scared to death of Jerry Lee Lewis.

Phoenix can't hit Cash's rumbling low notes, but gets the larger-than-life swagger that he brought to the stage, as well as the wounded isolation that often overwhelmed the singer out of the spotlight. It's a dogged, unrelenting performance, much as Cash was himself. Witherspoon is a revelation, showing a balance and maturity that's been missing from much of her previous work. Her June is no-nonsense but understanding, bruised but still loving, with a combination of sass and suspicion that can be heartbreaking.

As a strict biography, Walk the Line has its flaws. The film's analysis of Cash's problems can seem simplistic, and whole swatches of his career are ignored. Some facts and dates are twisted as well, but these issues are beside the point. The film isn't about his career as much as it's about his search for happiness. How he finds it with June Carter is one of country music's great love stories, and it's told brilliantly in Walk the Line.

-Daniel Eagan