Here, she is immediately befriended by two of North Shore High’s more good-natured social outcasts, the gothically inclined Janis (Lizzy Caplan, “Orange County”) and the teddy bearish Damian (Daniel Franzese, “Bully”). She hits it off with the duo right away, finding a kinship with the ostracized duo she didn’t expect. Soon the three of them are best friends, Cady getting a crash-course in the highs and lows of high school politics from the both of them.

But the newbe’s potent combination of beauty and brains also catches the eye of Regina George (Rachel McAdams, “The Hot Chick”), the cool and calculating Queen Bee of North Shore High. Regina realizes straight away that Cady has all it takes to take over rulership of the school, better to befriend the still clueless cutie then wait for her to figure out the social caste ladder at North Shore for herself. But when the new girl expresses interest in her former beau, school senior Aaron Samuels (Jonathan Bennett, TV’s “Boston Public”), Regina’s claws come out as she makes Cady believe Aaron still likes her, all the while claiming to be the teenager’s good friend.

At the urging of both Janis and Damian, Cady decides to fight fire with fire, insinuating herself within Regina’s clique of best friends to conduct sabotage upon the teen sweetheart’s social standing from within. Soon, to all outward appearance she’s every bit a member of The Plastics, the so-called name given to Regina and her friends, as stalwarts Gretchen Weiners (Lacey Chabert, “Lost in Space”) and Karen Smith (Amanda Seyfried, winningly making her feature debut) are. Strutting around the school in the latest fashion and the most perfect makeup, Cady enters “Girl World” with a high-heeled Machiavellian vengeance, turning friend against friend in a single-minded quest to end Regina’s rein as Queen Bee.

This is “Mean Girls,” the new film from “House of Yes” director Mark Waters, and it is easily one of the most pleasantly nasty surprises of this year. Inspired by Rosalind Wiseman’s Queen Bees and Wannabes: Helping Your Daughter Survive Cliques, Gossip, Boyfriends and Other Realities of Adolescence, “Saturday Night Live” featured writer and performer Tina Fey has constructed a topical and supremely funny screenplay bristling with insight. Girl World, as depicted in “Mean Girls,” is every bit as complex and full of shadowy espionage and innuendo as a CIA thriller, the routes the young women in the film take to get back at one another ingenuous in all their minutiae.

In all honesty, I missed this aspect of high school. Spending my time between cliques, I tended to move within worlds rather easily, not really cementing myself with any one group in particular. Granted, I didn’t exactly make the longest lasting friendships and save for one best friend, with whom I still converse on a semi-daily basis, most of the people I knew have long past from memory in these last few years. That said, it isn’t like I didn’t take stock of all the cliques, and like any reasonably smart kid I knew which girls to make friends with, which to keep on my good side and which to try and avoid.

A girl like Regina would definitely have resided within that second group. So popular that all the school mindlessly follows her every whim, she is just the type I would have done my best to be nice to so as not to engage her wraith. For when a Queen Bee gets angry there isn’t a safe hallway or backroom in an entire school safe from her fury, and that is exactly how McAdams plays her. Glistening behind a shiny Barbie Doll smile, she’s completely unafraid to kiss you on the cheek while planting a knife square in your back. But behind the immaculate façade is a cavalcade of insecurity and self-doubt, the pursuit of perfection causing ever-multiplying levels of paranoia that would be out of place in any other environment other than high school.

On the surface, Lohan has the easier role, the baby-faced and innocently sweet Cady the all-around “good girl” teen movies like this thrive on. But Cady isn’t really all that sweet and, by the end, she’s not remotely innocent, the complex politics of Girl World and the machinations behind her raise to power corrupting the good-natured young woman almost to the core. The actress, most recently coming off the eerily similar Disney film “Confessions of a Teenage Drama Queen,” portrays these contradictions with engaging aplomb. Cady is captivating, initially so downright effervescently likable that when her transformation into pure Plastic reaches its apex I couldn’t help but be crushed by just how far this gentle ingénue had fallen.

What most impresses me about “Mean Girls” is how twisted and malcontent the movie is. Fey and Waters dare it into completely uncompromising terrain, fearlessly changing gears and constantly pulling out the rug keeping the audience every bit as unstable as their characters. There is a nascent nastiness behind the humor that is as bitter and biting as any black comedy out there, Fey’s script venturing into dark waters unseen in a high school satire this good since Michael Lehman hit the nail on the head with “Heathers” almost two decades a go.

But, like that classic film, “Mean Girls” is far from perfect. Like many “SNL” writers making the transition to the big screen, Fey runs out of ideas long before the movie’s conclusion. Also, there is a third act riot by all of North Shore’s junior girl population that is just too far over-the-top, so uncomfortably unrestrained it took me completely out of the film. I also think Fey and producer Lorne Michaels wasted too much effort crafting parts for their “SNL” partners. In some cases, as with Fey (wondrously filling the shoes of a gifted yet sarcastically exhausted educator) and Tim Meadows (effortlessly playing the school’s easygoing principal), the casting works. But in other cases these bit parts are extraneous at their best, brutally unfunny at worst. And in the case of Amy Poehler (playing Regina’s wannabe-Plastics mother), her performance is just downright embarrassing, she’s so over-the-top and unfunny it’s nearly insulting.

And yet the film still works. From “House of Yes” to “Head Over Heels” to “Freaky Friday,” Waters has shown a knack for working with young women and girls and he’s definitely in his element here. “Mean Girls” moves with a precocious ferocity, each scene deftly moving to the next with expert comedic precision. Technically, the picture has a rough, almost documentary-like sheen to it, making the events going on in North Shore High almost like watching an episode of a PBS funded reality television series. Finally, there is an infectious quality to the mise-en-scene, and I couldn’t help but find myself wondering just what trick Fey and Waters had up their sleeves next.