The alluring Aussie is a passionate animal-rights activist who writes herself notes on her body. So yes, there is more to her than meets the eye

“I used to live in Kakadu, which is in Jabiru,” Isabel Lucas announces outside the Griffith Observatory in the Hollywood Hills. Although we’ve met here to go hiking, the 24-year-old actress speaks the gibberish-sounding place names so nonchalantly that it’s momentarily plausible that she’s referring to a distant planet and has chosen the observatory to make contact.

Lucas is an earthling—and an earthy one at that—born and raised in Melbourne (with stints in Queensland, Switzerland, and Australia’s Northern Territory), which means she’s not an alien in the extraterrestrial sense. She is, however, way out there. “Quirky” by her own admission, she says she likes to hike in Griffith Park because of the “energy of the trees and air.” At the sight of an overturned trash can, she launches into a lengthy discourse on the differences between jackals and dingoes. And though there’s an outstanding arrest warrant for her in Japan (the result of an anti-whaling protest she participated in), Lucas seems entirely unconcerned about the fact that the world premiere of her new film, Transformers: Revenge of the Fallen, will be held in Tokyo. “Oh,” she says, “it’s quite unlikely I’ll be arrested.”

Kakadu, it turns out, is an Aboriginal community where Lucas lived for a year during her seminomadic, bohemian childhood. “My best friend was Aboriginal,” Lucas says. “She taught me about ‘bush tucker’—the food of the land, the different things you could eat if you got lost in the bush, like grasses and berries. There’s this tree called the billygoat plum—the fruit is quite nice. It’d be a whole different story here. I don’t recognize any of these plants,” she adds, surveying the local foliage.

In fact, Lucas is dressed as if she’s never been on a hike in her life—a faded green eggs and ham T-shirt, wide-leg jeans, and green suede ankle boots. Her style is hippie-chic, but her face is pure Swiss Miss, a look she owes to her mother. “Mom spoke to us in Swiss when we were little,” she says—she calls the “singsongy” German dialect her first language.

Tourists on the trail don’t give her a second glance. If they were Australian, however, they might recognize her from the megapopular soap Home and Away. If they were avid gossip-rag readers, they might peg her as Entourage star Adrian Grenier’s ex-girlfriend, or as Transformers costar Shia LaBeouf’s mystery passenger when he flipped his truck and was cited for DUI last year (no charges were ultimately filed). The tabloids did their best to link her breakup with Grenier to a relationship with LaBeouf. “I don’t think it’s unusual to spend time with your castmate,” she says. “People instantly assume you can’t have a platonic friendship with someone of the opposite sex. I think this may be specific to L.A.—or America.” What’s clear is that Lucas, who is single, is as unrestrained in her affection for LaBeouf as she is in most things. “He’s got an awesome sense of humor and a big heart,” she says. “He’s got a lot to give. A really interesting character. And he’s also very passionate.”

It’s ironic that this nature-loving naïf is about to shatter her bubble of relative anonymity in a Michael Bay–directed blow-’em-up summer schlockbuster. Lucas plays Alice, a student LaBeouf’s Sam Witwicky meets at college. The Internet indicates her character is a Decepticon in human guise, but she’s loath to divulge any specifics: “Michael has us all on lockdown. He’s supersleuth about every detail.” Lucas landed the part after impressing Steven Spielberg with her work in The Pacific, the upcoming World War II mini-series he executive produced with Tom Hanks. Spielberg recommended her to Bay, and she took care of the rest.

Neither Transformers nor her next project, the vampire thriller Daybreakers, seems likely to diminish Lucas’ haute-granola spirituality. As we return to the observatory, she digs into her pocket and extracts a tigereye gemstone and a quartz crystal, two good-luck charms she says she carries with her at all times. I interrupt her to ask about a crudely drawn tattoo on her wrist that reads integrity. “Oh, it’s not a tattoo,” she says. “I wrote that on myself. I do that every day with a word I pull out of a basket my roommate has. Just as a reminder.” Perhaps the only thing better than a permanent personal mantra is an ever-changing one, especially for someone as delightfully free-spirited as Lucas. “And sometimes,” she confesses sheepishly, “I just write what I need to buy at the store—a grocery list.”

Hey, even a hippie girl’s got to eat.