Lynn Shelton’s Humpday boasted one of the more robust farcical plots in ages, so it’s tempting to expect more of the same from Your Sister’s Sister, her more laid-back follow-up. For the record, it basically invites it: Reeling from his brother’s death, Jack (Mark Duplass) is invited by friend Iris (Emily Blunt) to do some solo R&R at her family cabin. He arrives to find it already occupied by Hannah (Rosemarie DeWitt), Iris’ half-sister. A couple drinks later and Hannah, who’s gay, throws sexual preference to the wind for a hetero roll in the hay. Then Iris, who’s in love with Jack, shows up. Also, Hannah, who wants a baby, may have knowingly foisted a faulty condom onto Jack’s Malcolm Gladwell.
This is all resolved anticlimactically, and via a lazy montage set to sensitive guitar doodling to boot. But no matter: Shelton’s interest lies not in plot but in relationships, between the characters and the actors.
The heart of Sister is the sisters. Blunt was a last-minute replacement for Rachel Weisz, and by “last minute” we mean a couple days before shooting. Perhaps it’s merely a testament to Blunt and DeWitt’s acting chops, but they come off like people who’ve known one another their whole lives, not for only a large handful of hours. At one point, shortly after her arrival, Iris spikes butter into Hannah’s mashed potatoes. Hannah is quite loudly vegan, and is understandably irked by Iris’ dick move. But not that irked: the moment quickly deflates and the siblings quickly return to their mutually adoring relationship.
It’s a scene you don’t see in movies: an exchange that exists only between two people so comfortable with each other that they feel the need to occasionally fuck with one another, just to test the bond. Despite her gift for high-concept narratives, Shelton’s real interest is in behavior, and her methods—leading her actors but stopping short of literally putting words in their mouths—encourage them toward unusually focused (and believable) improv. It’s no wonder Blunt and DeWitt were able to instantly click: They had a great guide.