There's a scene in the concert doc "Katy Perry: Part of Me" where the titular hero, broke and "feeling lost" after knocking around for years from one record label to another, laments the loss of the "13-year-old with the blue guitar." The one who lived in Santa Barbara and wrote silly songs and dyed her hair a crayon box of colors.

"Is she still there?" Perry asks herself in a telling voice-over.

The moment represents a turning point for the singer. Music-business suits were looking to the era's early-millennium divas as they cooked up a persona for Perry, Easy Bake Oven-style. It was a (failed) recipe that amounted to: add 2 oz. of Kelly Clarkson's power pop, 1 heaping tablespoon of Ashlee Simpson's Autobiography and a dash of Avril Lavigne's benign snarl. Simmer over low heat for six months.

But Perry would not be packaged.

The California girl channeled her inner-teen, carving out a space that marries the hopefulness of nascent adolescence and the fearlessness of Alanis Morissette's Glen Ballard-driven catalog. ("I just want to be the first Katy Perry," she says earnestly.) Perry was in effect writing her own fairy tale, and it ignited a career.

Still, as the 3-D doc shows, it's her willingness to rewrite the ending in her "once upon a time" that has propelled her to the top of the pop firmament.

Because while Perry was collecting accolades -- five #1 singles from her sophomore album, Teenage Dream, an achievement shared only with Michael Jackson -- her storybook marriage to comedian Russell Brand was unraveling; "castles crumbling," as she sings on the film's roiling closing track, "Wide Awake."

With remarkable candor, cameras capture Perry on the world tour that follows her chart-topping second release ... and keeps the newlywed star far from her husband. In early glimpses, Brand is the supportive, protective partner, whisking Perry away after a handful of concert dates during her whirlwind run. But on a jaunt that spans hundreds of cities, the couple find it increasingly difficult to connect, a failing that's both geographical and emotional.

"I'm trying to save my marriage," Perry reveals between cheerful meet-and-greets with devoted KatyCats, many of whom come bewigged or dressed in costumes that pay homage to Perry's wide-eyed alter egos, from 13-year-old Kathy Beth Terry to the sweet tart of "California Gurls."

In another particularly compelling scene, Perry lies whimpering backstage on a cot. Her handlers do their best to console her, but it's clear they're concerned about what might happen if Perry can't muster the energy to perform for the thousands of fans who've filed into an arena in Brazil. After a few tense moments, the star signals to her makeup artist, and he sets about, rather literally, putting on her brave face.

The Brand chapter in Perry's story doesn't have a happy ending. Early in the film, the star and her sister detail the secular deprivations of their Pentecostal household: "Sister Act" is OK; "Alice in Wonderland" and "The Wizard of Oz," not so much. With those revelations in mind, the pop-up landscape Perry has created and documented onscreen feels like a rebuttal. A world populated by blue-haired princesses and tattooed princes.

So when real life interferes and the marriage dissolves like so much cotton candy, the viewer braces herself for the denouement. Yet Perry soldiers on, an evangelical pop star preaching the gospel to her legions of misfits and dreamers. It's a powerful lesson for a concert film. And the story doesn't end there.

"I want to go and write songs in the woods or something," Perry told MTV News late last month at the film's L.A. premiere.

Katy, now sporting darker, Grunge-inspired locks, has already hinted at a new direction and cited Madonna's penchant for reinvention. And reinventing herself is just what a princess taking charge of her own tale would do.

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