A person's life story is also the story of the people around him. Recognizing that is the secret to the greatness of "Walk the Line."

Unlike last year's so-so "Ray," "Walk the Line" shows how its hero, Johnny Cash, was shaped by the people in his life. It is a love story about Cash and June Carter, who did the movie the great favor of making Cash wait a decade before agreeing to marry him. And it is a story about finding one's voice, about a musician needing to discover the music he believes in most passionately because, as producer Sam Phillips tells Cash in a mesmerizing little speech, "That's the song that truly saves people."

Before that speech, Cash has half-heartedly sung gospel songs in an attempt to atone for the death of a brother he wished he could have saved. Afterward, he becomes a voice for the downtrodden and disconnected, and, in championing them, he finds his own voice.

It happens before our eyes in a riveting audition scene in which Joaquin Phoenix sings "Folsom Prison Blues." Tentative at first, Phoenix's voice becomes stronger and his eyes more steely as the song progresses. We're seeing the birth of a performer, and the scene needs Phoenix's performance to be magnetic. It is.

"Walk the Line" is about June Carter almost as much as it's about Cash (Reese Witherspoon, excellent). As written, Carter is a calm, elegant woman whose source of strength becomes clear only when we meet her warmly confident mother, Maybelle (Sandra Ellis Lafferty, in an indelible cameo). The movie knows Carter and Cash did not exist in a vacuum. So it shows us the characters through each other's eyes — Cash sees that Carter, a natural comedian and a spitfire, has a songwriting gift she doesn't value enough, and Carter sees that Cash, a junkie and adulterer, is a better man than he knows.

What's so smart about the movie is that it lets those themes emerge through the songs, which are woven into its fabric. "Ring of Fire," co-written by Carter, is about how frustrating it is to watch Cash drown in drugs and self-loathing. "Walk the Line" is Cash's pledge to Carter. "Folsom Prison Blues," written long before Cash saw the inside of a prison, is about feeling trapped and alone. I doubt if Carter and Cash actually fell in love onstage, but the series of duets that show their deepening affection makes sense because music is so integral to their lives — it helped them hang on when their lives were falling apart (especially Cash, who seems to have had the same pharmacist as Judy Garland).

Early in "Walk the Line," Cash's brother tells him, "You can't help nobody if you don't know how to tell a story." This fluid, big-hearted movie suggests that's an idea that guided Cash's life. There's no telling how many people were helped by Cash's songs — for starters, the thrilling prison scenes that bookend the movie suggest lots of people behind bars took comfort from them.

But, by weaving a life out of Cash's music, "Walk the Line" makes it clear that Sam Phillips was right. Cash's songs had the power to save at least one person: himself.