Your Sister's Sister

Increasingly ubiquitous Mumblecore-er Mark Duplass (Safety Not Guaranteed, Darling Companion, People Like Us) shows up for the fourth time this summer as a messed-up guy invited by his friend (Emily Blunt, The Devil Wears Prada) to decompress at her family's island cabin. There, he meets Iris' lesbian sister (Rosemarie DeWitt, "Mad Men"), and the three share some funny, unexpected emotional bonding. This is a very low-budget, low-key dramedy, but writer-director Lynn Shelton (Humpday) has a natural, instinctive feel for human interaction. 90 minutes R.