By Alex Tresniowski
January 14, 2008 12:00 PM

The details are different but the story is sadly familiar. At 2:46 a.m. on Dec. 27, Los Angeles sheriff’s deputies saw a car straddling two lanes on La Cienega Boulevard. They watched as its driver failed to signal a turn, then pulled the car over. And with that Mischa Barton, 21—best known for playing troubled teen Marissa Cooper on The O.C.—picked up a popular Hollywood accessory: her own mug shot.

Barton was arrested for driving “while under the influence of an alcoholic beverage,” according to the sheriff’s department press release, and for driving without a license. A deputy initially told PEOPLE after the arrest that Barton was also in possession of illegal narcotics, though officials later refused to confirm any details about drugs being involved. (Neither Barton nor her manager commented to PEOPLE.) Barton spent eight hours at the West Hollywood sheriff’s station before her $10,000 bail was posted; her mother, Nuala, was there when she was released from custody. “Her parents are mortified and horrified,” says a source close to Barton.

To others, the arrest is less surprising. A child actress who worked on Broadway before rocketing to fame on The O.C. in 2003, Barton fell off the radar somewhat after her character was killed in a car crash in 2006. After a breakup with hard-partying rocker Cisco Adler, she spent much of 2007 filming roles in several upcoming movies while insisting she is nothing like the reckless socialite she played on TV. “I never experienced [that type of] anything-goes chaos,” she recently told Maxim magazine. “I’d want to go out at 15 or 16, but I got it out of my system.”

Barton, who is a spokesmodel for Keds, also distanced herself from the young Hollywood social circuit once headlined by Nicole Richie, Paris Hilton and Lindsay Lohan—all of whom spent time in jail for DUI-related offenses. “I feel so, so different from those girls,” she told British Elle.

Yet the source close to Barton says she hit the town as hard as any other starlet. “All those girls are resentful of Mischa because they’re known as big partiers,” says the source, “yet Mischa is just as messed up but has always gotten away with it.” Until now. Barton is due back in court for an arraignment and likely faces probation and alcohol-education classes if convicted of drunk driving. But those alone, says the source close to her, may not be enough. “Mischa needs to go to rehab,” says the source. “Not just for her image, but for her health.”