There is something inherently disingenuous about Douglas McGrath’s “I Don’t Know How She Does It.” This is not, as much as the marketing for the film would have it, a spiritual sister to “Sex and the City” — even though it does steal its star, Sarah Jessica Parker and her plinking, sugary narration. Rather, this film makes the brave assertion that working women need not apologize for feeling fulfilled by their professional successes and then betrays that conceit for gooey sentimentality.

Parker plays Kate, a finance executive at a Boston investment firm. After impressing her boss (played by Pierce Brosnan, who looks completely out of place in this movie’s soft color palate) with a new account, she takes on a major, potentially career-making project that keeps her away from home. This movie’s thin plotting is more intentional than you would think.

Whether Kate and her boss pull off their big presentation to the bigwigs at their firm is beside the point — this is about seeing just how Kate pulls off her feats of working mother-wife magic.

Screenwriter Aline Brosh McKenna does well reining in Kate’s nearly spastic madness to comic episodes of upending sanity.

Part of this is Parker, who after years of traipsing New York in designer heels, lets rise to the surface the game, physical comedienne she can also be. An early scene of Kate contemplating the thought of head lice burrowing around her head is hysterical; Parker fully commits to looking foolish, something not all actresses are willing to do.

McKenna has been carving out a place for herself as the premier auteur of career-driven female comedies — you’ll recognize Kate’s unyielding determination in McKenna’s previous work, which includes “The Devil Wears Prada” and last year’s “Morning Glory.” She has a great talent for writing well-regarded, furrow-browed workaholics that manage to never grate; if anything, you become envious of their drive.

But here, her worst tendencies are given too much breathing room. The film is inundated with a veritable surplus of modern movie gimmickry: onscreen, animated text, elaborate daydreams and worst of all, an inexplicable faux-documentary setup where characters speak directly into the camera. Those secondary characters are pitiable outlines of real people, including the salty enough best friend (Christina Hendricks), the loathsome office weasel (Seth Meyers) and the out-of-touch, robotic co-worker (Olivia Munn).

In the film’s final act, she makes a screeching, nearly condescending reversal. McKenna builds a solid, breezy story of women, who by working hard, really do get to have it all — the career and the family. And then, just as she hinted at before in “Prada” and “Glory,” and outwardly does here, she turns the other cheek and into Greg Kinnear’s arms. In “I Don’t Know How She Does It,” a woman can have it all, but only if she wants her man just a little bit more.