Mumblecore — that somewhat pejorative term for very low-budget, improvised movies about self-absorbed 20-somethings — finally grows up in Lynn Shelton’s “Your Sister’s Sister.’’
The camerawork still isn’t anything to write home about — the images even pixilate once or twice — but this extremely well-acted dramatic farce of grief and betrayal actually has a resonance beyond its target demographic.
Mark Duplass — like Shelton, a key figure of the movement who has made his own films with his less photogenic brother Jay — is extremely good as Jack, an aging slacker who acts out at a memorial service marking the one-year anniversary of his late brother’s death.
The brother’s ex-girlfriend Iris (the ever-delicious Emily Blunt) — also his best friend who nurses a crush on Jack that he’s totally oblivious to — suggests he needs to chill out, and offers the family cabin in the San Juan Islands off the coast of Washington state.
When he arrives by bicycle, though, Jack discovers the cabin is hardly empty. Iris’ sister Hannah (Rosemarie DeWitt), a lesbian, has just broken up with her girlfriend of seven years.
Jack and Hannah bond over their losses, and in a drunken haze briefly do the nasty.
Then Iris shows up unexpectedly the next morning — and all three are quickly trying frantically to hide secrets from one another, with little success.
Movies have a long history of unlikely castings for siblings, but you can really believe DeWitt and Blunt as actual sisters whose deep bonds are tested by the poor judgment of Jack and, as it turns out, Iris.
Blunt, one of the best and busiest actresses working in films today, even makes you buy the concept that a smart woman like Iris would be smitten by a loser-ish guy like Jack.
And the performance by Duplass, who seemed so lost in a film like “Darling Companion,’’ lends credibility to the decidedly romantic notion that Iris’ love might help turn his life around, if she can get past what she sees as an almost unforgivable betrayal.
“Your Sister’s Sister’’ isn’t a perfect movie. Shelton (who also cast Duplass in the insufferable smug “Humpday’’) doesn’t always place the camera for maximum dramatic effect and takes very limited advantage of the picturesque setting.
But like her younger compatriot Lena Dunham’s HBO series “Girls,’’ Shelton’s work here suggests that mumblecore may be finding its way out of the artistic ghetto it’s placed itself in.