Drop the fresh-faced, wide-eyed Scarlett Johansson into a Park Avenue household complete with childish temper tantrums, marital strife and the infamous teddy bear “Nanny-Cam,” and you have the plot of “The Nanny Diaries.” Based on Nicola Kraus and Emma McLaughlin’s best-selling book of the same name, the movie boasts a gifted cast and showcases the dysfunctional lifestyles of upper class Upper East Side families but does little with either. Instead, directors Shari Springer Berman and Robert Pulcini offer up a bland and generic romantic comedy about a small-town girl making her way through New York City the best way she can — nannying.

When anthropology major Annie Braddock (Scarlett Johansson) finds herself without any career prospects, she accepts a live-in nanny position with the X family, who are referred to by their strange algebraic pseudonym throughout the movie. But taking care of the Xs’ son, Grayer (Nicholas Art), turns out to be more stressful than Braddock imagined, and she soon learns that the apparently idyllic Upper East Side of Manhattan masks some bizarre social behaviors that most anthropologists would kill to study first-hand.

Mrs. X, portrayed brilliantly by Laura Linney, enforces eccentrically strict rules — ranging from Grayer’s meticulously maintained high-soy diet to sanctions against riding the subway (“because of germs”) to preapproved “unstructured weekend activities” limited to visits at the Metropolitan Museum of Art and the Guggenheim. Mr. X (Paul Giamatti) philanders with women at the office and tries to appease his wife and son with money and trips to Nantucket instead of the genuine love and attention they each desperately crave. Both parents refer to Annie by her title — “Nanny” — as if her entire identity had been swallowed up by her new 24/7 employment.

After a rocky start, Braddock befriends the young Grayer, who has essentially been abandoned by his society-obsessed, socialite mother and his absentee, workaholic father. The two build a strong friendship and Grayer soon comes to love Braddock, making it all the more difficult for her to leave her employment with the abusive Xs.

Despite an engaging storyline and compelling characters brought to life by the talented actors, the script leaves much to be desired. There are few, if any, memorable lines, and the script serves more to advance the basic plot and prove how truly hellish the nanny life is than to flesh out characters or entertain the audience.

The various fantasy sequences — including a Mary Poppins-esque sequence in which Johansson sails into the sky with a red umbrella — range from overly cute to simply distracting. In several scenes Johansson observes Manhattanites as displays in the Museum of Natural History; the device might have worked better if they were shorter and appeared only in the movie’s first and last scenes to frame the plot in the middle. Instead, just as Johansson’s “desire to be an observer of life” keeps her from having one, the fantasy scenes force the audience into the role of observers as well, preventing viewers from becoming fully absorbed in the story.

Still, the cast does the best it can with the flawed script. Johansson’s role — which doesn’t grant her the proper forum for displaying her profound talents as an actress — mainly consists of gaping in awe at Upper East Side household dynamics and stammering meekly in response to her employers’ requests. Linney, on the other hand, shines as the jaded wife, affected mother and employer from hell. Her performance is nuanced enough to make the audience hate her in one scene and pity her in the next. Linney may have the most laughable line in the movie — “Nanny, you never mentioned you had a mother” — but she delivers it so ingenuously that viewers can’t help but scorn and sympathize with her simultaneously.

Chris Evans also delivers an amusing performance as the “Harvard Hottie” pursuing Johansson, who is forbidden to date while she is working for the Xs (and he more than lives up to the nickname). But ultimately the “The Nanny Diaries” is just chick-lit on the big screen. The scene where Evans asks Johansson, “If this job is so bad, then why don’t you just quit?” smacks of “The Devil Wears Prada,” and the rest of the movie feels like deja vu. Overall, a cute romantic comedy for mindless entertainment but probably worth waiting for on DVD.