When last we saw Michelle Williams, she was impersonating Marilyn Monroe for an Oscar nomination. Now she returns to vivify Take This Waltz, a movie that is essentially a pensive, gender-reversed The Seven Year Itch. Like that Billy Wilder comedy, this fraught romance from actress-turned-auteur Sarah Polley exists in a fevered state, an impossible dreamland where airlines provide gate-to-gate wheelchair service for anxious flyers, freelance writing affords a spacious garret, and young couples slow dance to Feist covering Leonard Cohen. This condition is also known as Canada.

So Polley's movie is unchecked by realism, and thank goodness: A new generation of actors needs big speeches and grand gestures to counter slovenly emotions and complicated defeats. Take This Waltz includes all these elements, but it's a messy packing job. The Polley-penned dialogue heedlessly weaves until it lands meticulously on the nose. It's a verbal field sobriety test. 

That electric unsteadiness begins when Williams' heroine, Margot, repeatedly meets cute with Daniel (Luke Kirby), first at a historical re-enactment, then in coach, and finally in a taxi's back seat, where she confesses she's married. Back home with her husband, chicken-cookbook author Lou (a splendidly grounded Seth Rogen), Margot engages in the same sort of impish flirtation, but with more baby noises and complacent wordplay. Take This Waltz is the first film I can think of that emerges from the Manic Pixie Dream Girl's point of view.

It is a roundly unsettling movie, because it portrays sexual chemistry as simultaneously irresistible and transitory—in short, cruel. Its visual motif is a camera swirling in helpless circles, making itself dizzy. This device is first deployed on a Toronto fun-park ride called the Scrambler, where Margot and Luke loop through strobe lights to the tune of the Buggles' "Video Killed the Radio Star," before the attraction grinds to a halt. It returns for the movie's most audacious sequence, a montage of erotic license set to Cohen's titular song, until the coupling wears itself out. Polley's movie has a self-excoriating subtext, like all the great breakup records we spin.  

There's been a lot of cultural noise lately about whether derision toward entertainment aimed at the female libido—Fifty Shades of Grey, or the Twilight movies that inspired it—is just another mask for chauvinism. Well, maybe. But Take This Waltz, itself undeniably flawed, is a reminder that desire is a serious matter, volatile and consequential. And movies, those permanent time capsules for fleeting moments, exist to tell us this. Pictures came to break your heart. R.

Critic's Grade: A-

SEE IT: Take This Waltz opens Friday at Living Room Theaters.