Reinvigorating the dangerous art of romantic-drama improvisation with Bergmanesque acuity, Lynn Shelton’s microbudgeted latest has the wind of unpredictability in its sails. It takes off at a dinner table, in an island-getaway house somewhere off the coast of Washington State. The hours creep by and the scene skips forward with giddiness. Two loners flirt over multiple shots of tequila: Jack (Mark Duplass, fully coming into his naturalistic chops) is still suffering over his brother’s death a year ago; Hannah (Rosemarie DeWitt) has been recently dumped by her longtime girlfriend and is burning with resentment. Neither was expecting the other to be there, but their emptiness makes them bold, and the night ends with them in bed together.
With the unexpected arrival of Iris (Emily Blunt, achingly open)—Hannah’s younger sister and Jack’s best friend—who harbors a thing for him, the triangle becomes a rare thing in American movies, one with points that truly pierce. Before you get the wrong idea, know that Your Sister’s Sister zings along like a comedy of nuance, the sex a heavy secret in the air. (It’s a vast improvement over Shelton’s self-consciously naughty Humpday.) The characters are believable, free of pop-psychologizing impulses—Duplass, an everyguy goofball, is especially valuable in this regard—and intimidated by the falseness of past relationships. Nothing about the movie is showy, except for Shelton’s palpable love of good people making a mess of things. Barring some late-inning coyness, it’s some of the truest, dinged-heart couples’ circling of the year.
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