Jessica Alba’s parking spot at the Honest Company, the four-year-old consumer-products start-up in Santa Monica, California, that wowed the tech community with a $1.7 billion valuation this summer, has a bright-green sign bearing her name. Before founding Honest, Alba was best known as the actress in roles such as a hip-hop choreographer with a heart of gold in 2003’s Honey and a strong-willed stripper in Robert Rodriguez’s Sin City franchise. I arrive for a tour at 3:32 P.M., and what transpires in the next 26 minutes is either a peek into Alba’s career as one of the tech world’s savviest businesswomen or the greatest performance of her acting career.

Alba’s cobalt-steel desk is part of an open-plan office that houses some of Honest’s almost 500 employees, all of whom have smiles on their faces and most of whom look to be in their 20s. “We hire a lot of people right out of college,” says Alba, whose current age, 34, makes her older than the office average. Next to Alba’s computer are towers of diapers featuring adorable cartoons. “It’s ‘the Paris collection,’ so we’re looking at French flags, the Eiffel Tower, a French bulldog that says ‘Le Woof.’ ” Alba approves the diapers but flags the tower’s salmon-colored packaging because the hue may skew too feminine for parents of boys. Behind her are new logo samples, each one a different shade of peach, but she’ll go through those later. She shows me a cozy, dimly lit room with scented candles where new mothers can pump their breast milk in private. And, in the hall, she overhears a conversation about a gifting suite the company may host at New York Fashion Week. She had hoped to create an editors’ lounge for makeup touch-ups and 15-minute massages but wonders if the $25,000 expense justifies the reach. (A single post viewed by her more than six million Instagram followers makes more of an impact.)

“Where’s the music up in here? Where’s RiRi and ‘Yonce?,” Alba shouts when we’re in the on-site photography studio. A mixed-race model with millions of adorable freckles is being photographed for a skin-care package and blushes when Alba gushes about her “modern beauty.” Alba suddenly checks the time and rushes the end of our tour, which includes the showroom, where new products are merchandised; the art department, where packaging is developed; the customer-service department, where employees answer up to 3,500 calls and e-mails per day.

And then, at exactly 3:58 P.M., Alba spins and says, “I’m sorry, but my four P.M. appointment is here.”

Director James Cameron, self-described god of the movie industry, gave Alba her big break in 1998 when he cast her as the lead in the short-lived TV series Dark Angel. He isn’t shocked by Honest’s success: “If you went back to the day I met Jessica and told me, ‘This girl is going to build a billion-dollar company,’ I would’ve said, ‘I believe it.’ ” Cameron’s production company auditioned more than 1,000 actresses for the part before he discovered her. Something about her glamorous sour puss made him press Pause. “She was slumped over with her hair in her face and a look of defiance. But when the camera hit her—wham!—there was such punk attitude.” (Alba admits she was a broody teenager—she has no Jell-O commercials in her credits.)

Dark Angel was set in the future (at the time, 2009 was the future), and her character, Max Guevera—a government-created, genetically enhanced super-soldier who escapes from a secret lab—presented Alba with more than a threat of stardom. “This was a $125 million production, and we were resting it on the shoulders of a teenager,” Cameron remembers. “She totally stepped up to the plate and didn’t fall or falter.” Alba worked 86-hour weeks in Vancouver, did many of her own stunts, and, Cameron adds, “never backed down from a fight. Early on, she had real integrity.”