Sexy, nasty and in-your-face when in-your-face was just becoming cool, The Runaways were THE ground-breaking all-female rock band, proto-punk pioneers in leather, spandex and bustiers.

A creation, or "conceptual project" of glam-rock producer/manager Kim Fowley, they were just breaking big when they realized that they wanted to be a band more than a "project."

And the rest is, or isn't, history.

The Runaways is a warts and all — especially the warts — musical biopic about the ensemble that gave Joan Jett, Lita Ford and Cherie Currie their start.

It lives and dies on the backs of three performances — Kristen Stewart is a ferociously sexy and butch Jett, Michael Shannon is a flamboyant and feral Fowley, and Dakota Fanning does her best to hang with them as unhappy and confused 15-year-old lead singer Currie, Miss Cherry Bomb to a generation.

An ugly decade — the 1970s — gets its due, in all its grungy pre-grunge in photographer-turned-director Floria Sigismondi's drama. We meet the Currie sisters (Riley Keough plays sister Marie) as Cherie is having her first menstrual moment. That sets the tone as Sigismondi, who also scripted this, emphasizes the ugly — their unhappy childhoods and the nasty dog-eat-dog scene these teenage girls tried to break into.

Joan Larkin starts calling herself Joan Jett, buying men's biker leather and teaching herself the electric guitar. She stammers an introduction to Fowley at a club, pitches an all girl-band idea. He hooks her up with drummer Sandy West (Stella Maeve). And after they pester him, he drags those two out clubbing in search of other bandmates. That's where they meet the Bowie-obsessed blond, Currie.

Then, the Svengali Fowley delivers his patter.

"You dogs need to get dirty," he growls. "This isn't about women's lib. It's about women's libido."

He berates them, preps them for hecklers by hurling trash and feces at them, and puts them — underage — on the road where they will sink or swim.

They swim, and Sigismondi's film does too, as long as it is following their Fowler-fueled rise. The energy flags as the movie slumps into the downside of their arc — the inevitable egos and drugs and family problems.

This is also where the movie is most focused on Fanning, who gives her most adult performance but is still not on a level with Stewart or Shannon.

Stewart loses her lip-biting winsomeness and brings the heat as Jett. And Shannon, with all the best lines, walks off with the movie.

It's not great cinema any more than The Runaways were "the biggest thing since The Beatles" (Fowley's pitch). But it is a well-acted and vivid re-creation of a dark, downbeat era when "girls don't play electric guitar," and you had to be someone pretty tough and pretty special to try it.

See for yourself.