The time is 1987, and 13-year-old Jenna Rink (bright newcomer Christa B. Allen) is suffering through the embarrassments of middle school, yearning without much success to fit in with the popular clique of girls, led by snobby Tom-Tom (Alexandra Kyle), while looking from the outside in with best friend Matt (Jack Salvatore Jr.). When a misunderstanding with Matt leads to a falling-out on her birthday, Jenna uses a packet of wishing dust to make a plea that she be "thirty, flirty, and thriving." Much to her fear and amazement, the wish comes true.

A now-adult and curvy Jenna (Jennifer Garner) awakes in a spacious Manhattan apartment to discover that she now has a lunkhead boyfriend, Glenn (Maz Jobrani), and is magazine editor for trendy fashion magazine "Poise." Best friends with coworker Tom-Tom, who now goes by Lucy (Judy Greer), Jenna doesn't like what she learns she has become: a bitch who ruthlessly steals story ideas from a rival publication and fires people at the drop of a hat. Jenna tracks down Matt (Mark Ruffalo), now a photographer engaged to be married, who explains that they haven't talked to each other in seventeen years. As she tries to make up for lost time and right the things she has wronged, Jenna finds herself realizing Matt is her one true love—a destiny she may have lost forever.

Directed by Gary Winick (2002's "Tadpole"), "13 Going on 30" brings nothing new to the recently resurgent "body-swapping" genre and generally plays things safely. If you've seen the trailer and TV ads for the fi lm, then you know exactly what to expect. At the same time, there is a comfort with watching "13 Going on 30" because, although few plot developments come as a surprise, the movie proves to be in good hands right from the start. The ten-minute prologue set in 1987 gets the era and angst of being a teenager just right, aided immeasurably by a nostalgic waves of '80s pop hits that carry straight through into the present-day story ("Love is a Battlefield" by Pat Benatar, "Jessie's Girl" by Rick Springfield, and "Thriller" by Michael Jackson feature prominently).

Once the clock moves forward to 2004 and Jenna wakes to a world she doesn't know, Jennifer Garner must carry the film almost solely on her shoulders, something she is more than capable of. The role of Jenna, who is still a teen even though she may look thirty, is tricky, indeed, and Garner is superb in ratcheting up honest humor out of the situation without going overboard and getting too cutesy. Underneath the comedy, how ever, is something far more poignant and touchy, as Garner must deal with the realization that the unsavory person she has become is not at all who she is at heart. As the adult Matt, Mark Ruffalo (2003's "In the Cut") may just be playing the obvious romantic part of "the guy," but he does it extremely well, particularly when asked to face the internal wounds of the past, when Jenna abandoned him for a group of shallow friends and never looked back.

Kudos should also go out to a screenplay by Josh Goldsmith and Cathy Yuspa that never exaggerates or stereotypes the evolution of a character who has aged seventeen years. Lucy, for example, played by the underrated Judy Greer (2002's "Adaptation"), was a bad apple as a child and still has some of the same back-stabbing characteristics as an adult, but it is rarely overplayed and she is never treate d as an outright monster. If the overall premise is handled with honesty and wit, the script does flounder by missing a great many opportunities for Jenna to react to the advanced technology that goes along with waking up two decades later. Save for one running joke with cell phones (when Jenna hears musical rings while on the streets of New York City, she thinks she is going crazy), little is done with this potential comic goldmine. The final scenes, while simple and gratifying, also might have benefited had they not arrived so abruptly; a few storylines are left dangling in director Gary Winick's rush to get to the end credits.

If "13 Going on 30" pales next to "Big" (a warranted comparison), it is a worthy enough successor that should satisfy a wide audience in search of a heartfelt comedy that avoids laying its sentimentality on too thick. Best of all is Jennifer Garner, who steals her every scene without even trying as she inhabits a memorable role one cannot help but fal l in love with. "13 Going on 30" is undemanding, featherweight fare, but it is genuine and engaging enough to overcome its more commonplace aspects.