Your Sister's Sister

Your Sister's Sister might be an indie movie (actually, there's no 'might' about it – it is an indie movie) but it has the length, breadth and width of a High Concept mainstream romp. If Shelton thought Humpday, a comedy about two straight male friends who decide to have sex with each other, was a stretch to pull in a mainstream audience she should have no problems with her latest.

It's a year since his brother died and Jack (Duplass) is still in a funk, as he remembers a different person to those who queue up to deliver glowing toasts to his memory. Encouraged by his brother's ex-girlfriend Iris (Blunt), to whom he's secretly attracted, to take a break at her family's island home, Jack looks forward to the peace and quiet. But that's not what he gets: Iris' half-sister Hannah (DeWitt) has taken up residence as, just out of a nine year relationship, she too needs some headspace. Drunk on tequila one night, Jack propositions the lesbian Hannah and she takes him up on it. But then Iris shows up.

In life, it's rare to find someone hilarious the moment we meet them. Most of the time it's only when we get to know them and get used to their sense of humour that the funny emerges. Same here. Iris, Jack and Hannah aren't funny at first, as Blunt, Duplass and DeWitt's ad-lib delivery and Lynn Shelton's dialogue is rather loose and awkward, but then they grow on you. By the time the midnight drinking scene unfolds, which has a well-observed natural progression, we want to hang out with these people and hear their stories. Without trying too hard, the three put a smile on our faces. It's never thigh-slapping gags, but a constant humorous tone.

But when she's not trying to make you smile, Shelton finds real tenderness; when Iris creeps into Hannah's bed for a heart-to-heart in the middle of the night it has such a natural atmosphere it's as if we're eavesdropping on a very private conversation. The highest compliment you can pay a director is when you forget you're watching a movie – at times here Shelton has a knack of slipping you into some very intimate moments, like we're stuck in the corner of the room.

The performances are flawless. Blunt and DeWitt are lovely and then there's the charming Mark Duplass. If Greta Gerwig is the Indie Queen then Duplass is the King; he's not long for the title though - upcoming films with Chris Pine (People Like Us) and Lawrence Kasdan (Darling Companion) will see to that.

Three people, one house: there's only so much you can do with that set up before issues start being forced and Shelton can be guilty of that towards the close. Maybe the writer-director could have explored Jack's deep-seated feelings about his brother further but she barely touches it after his initial emotional outburst. But those nit-pickings aside, this is a grower.