Seattle filmmaker Lynn Shelton's appealing comedy "Your Sister's Sister" is an actor's movie, offering the small-scale pleasures of a good story well-told. For most of its running time, it has only three characters. Jack (Mark Duplass) is restless and unhappy, still grieving for his brother a year after his death. Iris (Emily Blunt), Jack's best friend, takes pity on him and suggests he go spend some time at her family's vacation home on a nearby island, for solitude and self-examination.

But when Jack arrives, he finds someone unexpected: Iris' sister Hannah (Rosemarie DeWitt), who's just ended a long-term romantic relationship and was seeking a little solitude of her own. It's an awkward situation, made more so by the unannounced arrival of Iris the next day: one trio, three pairs, all altered by the events of one night.

Filmed in the picturesque San Juan Islands by cinematographer Ben Kasulke, "Your Sister's Sister" unfolds like a story told to you by your best friend: you believe every word. The actors, who improvised much of their dialogue (they're listed as "creative consultants" in the credits), never hit a false note — each making their character someone flawed yet appealing. Duplass' Jack (who has a habit of suddenly exhaling by blowing, as if he's quietly releasing built-up steam) is a rumpled, impetuous charmer, constantly doing the wrong thing but always meaning well. DeWitt, dryly sardonic, clicks instantly with his rhythms as she creates a moody woman who nonetheless knows how to laugh at herself. And Blunt, who's as always sweetness personified, gives a small master class in acting without words: accepting an apology with a small, silent nod; quietly gazing with incandescent love.

"Your Sister's Sister," evidence of Shelton's growing mastery of storytelling, ends almost before you want it to, with a question that isn't answered — which is, on reflection, exactly how it should be.

Moira Macdonald: 206-464-2725 or mmacdonald@seattletimes.com