At 18, Kristen Stewart has already played an aspiring musician for Sean Penn (Into the Wild) and done time as De Niro’s sexually adventurous daughter (What Just Happened). “I usually do indies,” says the L.A. native. With this month’s Twilight, however, she ventures into worldwide-event territory as Bella—your average American girl, who moves to a small town and falls mad-crazy in love with a vampire. The movie is based on the first entry of the wildly popular series (10 million copies sold and counting), a fantastical epic for goth chicks and adults mourning the loss of Harry Potter. “The series has this huge fan base,” says Stewart. “And they have very specific expectations. They’re supportive. But they’re crazy.” How so? “It’s like we’re their pets. If we’re bad, they’re going to punish us.” Uh, creepy. But if she can handle Sean Penn, rabid girls with fangs shouldn’t be a problem.