Up until now, whenever I said that a film is like a sitcom, I always meant it in a negative context. I now realize how shortsighted that was on my part, because the truth is there have been and still are very good sitcoms being aired. I came to this realization after seeing Your Sister’s Sister. This movie plays like a particularly well-written sitcom, manufactured and unrealistic but nevertheless funny, nicely cast, decently performed, and ultimately redeemed by the charm and likeability of its characters. When necessary, it eases up on the laughs and allows for some good poignant moments. The events depicted in the film exist primarily in the minds of writers, although that isn’t necessarily a bad thing; all that matters is that we become invested in the plot, that we feel something for the players and their roles, and that we’re entertained.

We’re introduced to a man named Jack (Mark Duplass) as he loses his cool at the memorial service of his brother Tom. He continues to grieve a year after the death, having lost control of his emotions and his ability to work. Iris (Emily Blunt) is Tom’s ex-girlfriend and Jack’s current best friend; understandably concerned over Jack, she offers him the keys to her family’s secluded cabin, which is nestled in a picturesque island somewhere in the Pacific Northwest. Jack reluctantly agrees to go. When he arrives, he’s surprised to see someone else, a woman, staying in the cabin. She too is just as surprised to see him, and she wastes no time in threatening to ward him off with a boat paddle. The confusion is quickly cleared up; the woman is Iris’ sister, Hannah (Rosemarie DeWitt), a lesbian who’s in her own emotional rut following an abrupt end to a seven-year relationship.

That night, the two begin bonding over a bottle of booze. As they sat at the dining room table downing shot after shot, I was amazed to find that their dialogue became more absorbing as they got drunker. It had more to do with the delivery than with the actual choice of words; with its free-flowing style, I had a sneaking suspicion that writer/director Lynn Shelton allowed DeWitt and Duplass to veer away from the finished script and indulge in improvisation. If this was the case, these actors deserve extra praise. Anyone can breathe life into a role by following a script to the ink, but it takes a special kind of actor to spontaneously create his or her own dialogue while keeping it consistent with the story at hand. If this wasn’t the case, then Shelton should be commended for writing especially believable dialogue.

We fully expect that Jack and Hannah will lose all their inhibitions and have sex, and so they do. We may even expect some of the inevitable consequences, none of which I will examine in great detail. But don’t delude yourself into believing that Your Sister’s Sister lacks surprises. I’m not referring to outlandish twists of fate dependent entirely on actions; I’m referring to unexpected decisions based on emotions. The rest of the film, which cannot be discussed without the issuing of a spoiler warning, is refreshingly mature and level-headed in its approach to a contrived scenario. You know in the back of your mind that what happens is rather unlikely, but you still savor the sharpness of the dialogue and the evolution of the characters. You also come away with the hope that, if such a thing were to happen in real life, the people involved would handle it as well as the people in this movie.

Iris will eventually reenter the picture. This creates a good deal of humor, as both Jack and Hannah are torn over their decision to keep their one night of passion a secret. The relationship between Iris and Jack is fairly solid and nicely developed, but what I responded to more was the relationship between Iris and Hannah. They have their issues with one another, as most siblings tend to have, but that doesn’t mean they’re treated as soap opera caricatures, in which they’re needlessly vindictive towards each other. We see a fairly convincing depiction of two women who love each other despite the fact that they’re different. Even when Iris mixes some butter into a bowl of mashed potatoes and knowingly serves a spoonful to the vegan Hannah, nothing devolves into a prolonged episode of nasty sibling rivalry.

Some audiences are not going to respond well to the ending, as it leaves one very big question unanswered. From my perspective, the emotional closure more than makes up for the lack of narrative resolution; we may not know the outcome of a particular scenario, but we do know how all three leads will respond should it turn out that way. In other words, everything that needs to be said is actually said before the end credits start to roll. I now realize that my initially straightforward review has long since become annoyingly vague, but Your Sister’s Sister is the kind of film that demands a certain degree of secrecy. Rightly so; some movies are better the less you know about them beforehand. If you’re receptive to the material, improbable though it may be, you should be able to leave the theater feeling perfectly satisfied.