Like its own, slightly less sinister version of The Cabin in the Woods, Your Sister's Sister is a film that emphasizes the realizations and revelations that are bound to occur in an isolated setting. Written and directed by Lynn Shelton (whose other notable work was 2009's Humpday, also starring Mark Duplass), the minimalism of the movie's production barely crosses one's mind because of how engaging, yet uncannily natural the dialogue is.
Opening at a commemorative get-together for Jack's (Duplass) brother, Tom, who died a year ago (though we never discover the cause), a mutual friend named Al (Mike Birbiglia, the only other character in the movie to have dialogue besides Emily Blunt, Rosemarie DeWitt and Duplass--unless you count the waitress who asks Jack if he wants more coffee), speaks fondly of Tom. As he recounts seeing Hotel Rwanda with him (I love when film allusions are made in other films, it should really happen more often), he points out that, afterward, Tom immediately started volunteering for an organization to help Rwandan refugees--illustrating that he was the type of man who actually put his convictions into action instead of just talking about them.
Jack, however, points out that it was another movie that changed Tom's life course: Revenge of the Nerds. He explains that Tom's eyes were opened to the benefits of being a "nice guy" as opposed to the bully he really was. Jack's insistence on this fact makes everyone grow increasingly uncomfortable, except, of course, his best friend and Tom's ex-girlfriend, Iris (Blunt).
After Jack stalks out of the room, Iris follows him and suggests that a retreat to her father's cabin might be in order so that he can possibly get the chance to gain some perspective on the past year. With no other viable solutions to his misery in mind, Jack accepts Iris' offer and heads to the cabin with his bicycle (per Iris' insistence and also perhaps to showcase the stereotype that you can take a ferry from Seattle to anywhere else in the Pacific Northwest vicinity).
Upon arriving, Jack is surprised and intrigued to find Hannah (DeWitt, who will always hold a special place in my heart for her role as Don Draper's East Village mistress, Midge, on Mad Men), Iris' sister, even though Jack isn't aware of that familial connection as he watches her strut around the house without pants on. When Hannah catches him lurking, she sneakily lunges at him on the porch with an oar. Once he explains himself and they are formally introduced to one another, their shared love of alcohol is quickly uncovered.
Inviting Jack to join her in a bottle of tequila, Hannah is drunk enough to inform him that she just ended a seven year relationship with a woman named Pam. As she relays the story, Jack learns that Pam cheated on her with another woman. Appalled--and evermore inebriated--Jack confesses that if he was "differently equipped" or if she was "differently inclined," the night would probably go in another direction. Hannah gamely responds with an affirmative reaction to taking him up on his offer. A bit taken aback (but nonetheless aroused), Jack asks if she's certain she wants to go through with something they'll undeniably regret in the morning. With Hannah's reassurances that there's really no legitimate reason why they shouldn't go through with it (he's single, she's single--lesbian aspect aside--fuck, it's like the simple math of 2 + 2), the two of them head to the bedroom.
As they become marginally engrossed in the throes of passion, Hannah reminds Jack that they don't have a condom. Vaguely miffed, Jack suggests saran wrap (it's somewhat reminiscent of that scene in Shopgirl where Jeremy advocates using a "baggie"--oh men and their utter insensitivity) as an alternative. Ignoring his attempt at problem-solving, Hannah goes to retrieve one from some unknown part of the house. Passionlessly, Jack gives approximately five thrusts before passing out and subsequently awakening to the sound of Iris walking toward the house with groceries. Frantic, Jack starts shouting cover stories at a barely coherent Hannah as he goes to put on some makeshift workout clothes so he can pretend as though he's been on a run.
When Iris enters the house to see Hannah, she is completely overcome with joy--an emotion that is tempered when Hannah tells her that she broke up with Pam. At that moment, Jack enters the room looking as though he just went for a swim in his clothes. Feigning shock over seeing her, Jack proceeds to act as unnatural as possible, though Iris is utterly oblivious to it, apparently accustomed to Jack's zany ways. As the day progresses, Jack steals away a few moments alone with Hannah to discuss the fact that Iris can never know what happened. Picking up on Jack's underlying emotions, Hannah questions if has feelings for Iris. Jack quickly and too strongly denies having any such sentiment.
Shrewd elder sister that she is, Hannah instantly grasps the true reason why Jack doesn't want to tell Iris. Later on that night, as it turns out, Iris crawls into bed with Hannah and, as they get to talking about Jack, answers honestly when Hannah asks if she likes him. Iris admits, "I think I'm in love with him." A look of alarm subtly spreads across Hannah's face as she realizes the gravity of what she's done. With this recently acquired information, Hannah confronts Jack and agrees that his original plan to keep their tryst a secret from Iris is probably best.
As the plot continues to unfold, the complexities of each character play off of one another to perfection--revealing an unexpected twist in the story that proves you don't need a high budget to create high drama.