If you've heard of the Duplass brothers, then you're probably aware of a semi-hip movement known as mumblecore. If you haven't heard of it, well don't worry, you really aren't missing out on that much.

The Duplass brothers have moved on since then, with the pair directing the quirky comedies Cyrus and Jeff, Who Lives at Home.

Someone else considered part of this movement is Your Sister's Sister writer and director Lynn Shelton. But she too has moved on from mumblecore with this sweet comedy drama, which also features... (very slight drum roll) Duplass bro Mark, but with his acting head on this time.

The pair may have moved away from the mumblecore philosophy, but they prove with this film that they're not quite prepared to let go of their indie roots.

It's been just a year since his brother's death and Jack (Mark Duplass) still isn't in a good place yet mentally. His best friend Iris (Emily Blunt) tells him he needs to get away for a while and sort his head out, and she knows the perfect place to go. Her father has a remote cabin on an island that is currently lying empty, so it would act as the best retreat for him. Jack agrees.

So off he heads into the middle of nowhere, where he eventually finds the cabin. The problem is, there's already someone else in it. It transpires it's Hannah (Rosemarie DeWitt), who just so happens to be the half-sister to Iris. She's making her way through a bottle of tequila, drowning her sorrows having just broken up with her girlfriend.

Despite it being an awkward situation, Hannah insists that Jack stays, so he does. The pair end up making further progress with the alcohol, which results in them getting surprisingly touchy feely.

The next day, the pair get a visitor – Iris. The awkward-o-meter goes up a notch or three, especially when she reveals to her sister that she's actually really into Jack.

The latest line in Scandinavian bedding proves yet again it's very much style over comfort.

There may have been a time when this film would have been one of those indie films that sneaked under the wire for many, but with Emily Blunt on board, it became a more commercial project. That's not to say it's worse off, just that it may well have been slightly different.

So what is My Sister's Sister then? Well, it's a nicely written and well-observed piece that benefits from great performances from its three main leads. Duplass possibly shines the most, giving a pleasing account of himself in what is essentially the lead male romantic role. Yes he is the only male lead role, but that shouldn't detract from his charming performance. All this and he can direct too – his mother must be very proud.

In fact all three leads probably lift the material to another level just from the strength of their performances alone. All are extremely likeable, and the uncomfortable interaction between all three makes for enjoyable viewing.

And as it is essentially just the three of them on screen in one locale, you can see the piece translating really well to the stage. That said, Shelton does enough so that it doesn't feel claustrophobic or overly dramatic.

It may be the most mainstream project that both Shelton and Duplass have worked on, but there is still an undercurrent of indie-cool to be found here too. That said, it also proves that the pair are more than ready for more commercial projects.