Your Sister's Sister is a sweet story about siblings, grief and complicated relationships. It begins at a gathering on the one-year anniversary of a death, where we meet the brother of the departed, Jack (Mark Duplass), who isn't taking it so well, and the dead brother's ex girlfriend, Iris, (Emily Blunt). Straight away, you know you're watching an uncomfortably realistic indie film when Jack makes one of those drunk, rambling toasts that causes you to hold your breath and pray for it to be over.
This first scene is cool for a lot of reasons, chiefly because it features a cameo by the comedian Mike Birbiglia, who seems to be playing a character very much like himself. Secondly, everyone is drinking. Writer/director Lynn Shelton understands something important about how people in their thirties interact with one another. So many of us find it impossible to get real without the sauce, and intimacy through alcohol is an unspoken theme throughout the film.
In the months following the brother's death, Iris and Jack have become best friends. Jack is in bad shape, so Iris sends him to her family's cabin on an island off the coast of Washington State to get his head together. He arrives under the cloak of night, only to discover the cabin is already occupied by Iris's sister Hannah (Rosemarie DeWitt). She thinks he's an intruder and tries to hit him with an oar, he's bumbling and adorable, you know the drill.
Jack and Hannah sit down with a bottle of tequila and things get realer. Hannah's just left a seven-year relationship with a woman, and in their conversation, Jack reveals his own grief and insecurities. They're attracted to each other, it would seem, and the night culminates with a clumsy hookup that unfolds on screen in real time. The sex manages to be much more hilarious and tender than graphic, and when it's over, you can almost see them glimpsing tomorrow morning's embarrassment.
Jack and Iris are in love, of course, so when Iris unexpectedly arrives at the cabin, Jack pulls a total guy move and conspires with Hannah to keep their tryst a secret. What follows from there is a complicated dance of feelings and deception between Iris, Jack and Hannah. Iris and Hannah are the kind of sisters who sleep in the same bed and whisper about boys, and it would be awful if anything jeopardized that relationship, right? Remember that Jack knows what it's like to lose a brother.
The movie relies a lot on improvisation and long takes, and it almost always works. Iris wants to tell Jack that she's in love with him so badly, but she's scared that their relationship will change, or maybe she'll be rejected, and there's the memory of the dead brother looming over both of them to consider. Her conflict feels tangible and real, and it's made all the more awful to watch because everyone else in the room knows something that she doesn't.
That the movie devolves into melodrama and romantic comedy tropes by the end is only a little disappointing. All bad romantic comedies seem to hinge on a fake problem. "I want to tell him how I really feel, but I just can't." "I want to be with her, but I just can't." There's a little bit of that going on here.
In the end, there are only a couple of ways out of this movie: Either Iris and Jack get together, or they don't. Romances between best friends are the most romantic ever, because you get to say, "I love you" on the first day of your relationship. If they don't get together, well, the friendship will probably never be the same and the brother is still dead. And what will become of Hannah? What if she's pregnant? Wouldn't that be weird?