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There’s a handful of holy-shit revelations in the final chapters of Your Sister’s Sister, Lynn Shelton’s follow-up to her 2009 misfire Humpday. And it ends on an Inception moment, leaving an “Is she or isn’t she?” question unanswered. But giving away too manyplot pointsor any, reallywould ruin the gasps that Shelton’s small but absorbing film elicits.

Fans of Humpday, if there are any, won’t be surprised that Your Sister’s Sister ultimately revolves around sex, specifically a one-time experience. It begins with a gathering on the first anniversary of someone’s death. Shelton doesn’t specify how Tom, brother of Jack (Mark Duplass, indie’s rumply answer to Jason Segel), died, but an argument breaks out over how he lived. After one friend deifies him, Jack, who’s had a few drinks, corrects matters: Tom was kind of a dick.

Afterward, Jack’s best friend, Iris (Emily Blunt), tells him he’s a wreck, and prescribes some time alone in her father’s cabin, where Jack is “just going to sit.” But when he gets to the house, Iris’ sister Hannah (Rosemarie DeWitt) is already staying there. She reluctantly lets Jack stay, eventually confessing that she just walked out on her seven-year partner. They bond. Then, the next day, Iris shows up unexpectedly.

Thankfully, Shelton leaves behind most of her mumblecore tendencies (her camera’s still wavering, ever so slightly). Her script feels scripted but never false, with dialogue—mounds of it, in fact—that is unerringly, refreshingly natural. “It is what it is, and it sucks,” goes one line you’ve probably heard or said at least once in your life. The plot-igniting sex scene, too, is also awkward but believable. “Oh shit, I squealed—sorry,” the squealer says.

Your Sister’s Sister is at its heart about love and its complications, and about desires one may not be sure should be revealed. Everyone’s deep-down secrets are unearthed here, though, followed by perhaps a few too many quiet-reflection scenes accompanied by a guitar-plucky, angst-is-us soundtrack. Duplass has never been more endearing—even with all of Jack’s issues—and Blunt and DeWitt make realistic, likable, intimate sisters. (Blunt’s British accent is even explained.) There’s verité with nary a mumble.