It is a biopic based on the drug and partying days of the 1970s teen girl band The Runaways that launched the careers of Joan Jett and Cherie Currie.
Stewart plays Jett, Dakota Fanning is Currie and Elvis Presley's granddaughter Danielle Riley Keough, in her first feature film, was cast as Currie's sister, Marie.Photos of Stewart have become highly-profitable business because for The Runaways role she chopped off Bella's long locks and now sports Jett's trademark short, black hairdo.
The first Runaways star I spoke to was the very sweet Keough, who travelled the world as a model for Christian Dior and other top tier fashion houses before making her film debut in The Runaways.
Talk turns to the music she like to listen to.
"I like older music", she says.
"Bob Dylan, Daft Punk."
What about Elvis?
"Yeah," she laughs.
Fanning is almost unrecognisable as Cherie.
Her hair is bleach blonde, although you can see dark roots coming through.
What has happened to the girl that made me cry in I Am Sam?
"How do you like your hair?" I ask.
"It's a wig," she replies.Her PA was correct, through the trailers she appears, a replica of a young Joan Jett.Stewart is dressed in tight leather pants, leather jacket, sneakers and puffing on a cigarette.
"It is weird when you are nostalgic for a period you have never lived," Stewart, revealing her love for the 1970s, says.
"The 90s? Alright, whatever.
"The 70s? More was happening."
After an 18 minute chat Stewart was off to shoot a scene, protected by four large men carrying larger umbrellas.
Leaning on the Charger is Nick Eversman, a skinny 23-year-old actor cast as Rocker Boy, a dude who engages in a passionate kiss with Jett outside of Bingenheimer's club.
This is a huge gig for Eversman, who proudly admits his day job is dressing up as a prawn outside of a Bubba Gump seafood restaurant adjacent to Universal Studios.
When I caught up with Eversman he was at the catering tent chowing down on an plate of unrecognisable food.
I asked the obvious question to a dude who was about to kiss the most famous teenage girl on the planet.
"How is your breath? Are you sure that food will not make your breath smell?" I ask.
"I made sure to brush my teeth today", he replies.
"I did bring my toothbrush with me."
To my surprise, Stewart and Eversman have not discussed their onscreen kiss. There is no rehearsal. When the cameras roll they will go for it.
"All the script says it is 'passionate', Eversman says.
The second obvious question ... will tongue be involved?
Eversman is a gentleman.
He says he will wait to feel what Stewart offers.
If he feels tongue then he will offer his.Late into the night The Runaways director Floria Sigismondi yells "action" and, with the real Joan Jett standing among the film crew, the lip action starts.
The teenyboppers are still on the corner hopeful of a signature.
The paparazzi are there to photograph Stewart and Eversman kissing so tabloid magazines can run Kristen Stewart's New Boyfriend stories.Was there tongue or no tongue?
The Runaways releases next year so go buy a ticket".