“The One I Love” is pretty good as a movie and sublime as an exercise, especially an acting exercise. Just describing details about the story will require a huge spoiler alert, which I will insert below before giving away some of what happens in the film (omitting the ending, of course). But first, we can mention the acting challenge presented by the film. Two actors are on screen for almost the entire running time and are required to display small but distinctly different characteristics to help us and the characters keep everything straight. That is a pleasure to watch on a whole other level aside from the storyline. Elisabeth Moss (“Mad Men”) and Mark Duplass (“The Mindy Project”) play Ethan and Sophie, a married couple seeing a therapist (Ted Danson) for counseling. Ethan remembers with great warmth when they first met, and impulsively went for a swim in a stranger’s pool. The sense of fun and freedom they had is something he misses. Sophie is having trouble trusting Ethan again because he had an affair and he is embarrassed and defensive. “I felt like our happiness used to be so easy and there used to be so much of it,” she says sadly. The therapist recommends a weekend getaway to a beautiful, remote cabin, assuring them that every couple he has sent there has returned “renewed.”

They arrive at the cottage, which is lovely, and discover that it has a guest house. SPOILER ALERT: As each of them enters the guest house separately, they encounter what they at first think is each other, but then realize is some other version of the person they married, a little brighter, sweeter, more considerate, more agreeable. Sophie’s new Ethan apologizes sincerely and contritely for his transgression and paints a portrait of her to show his devotion. Ethan’s smiling, slightly Stepford wife-ish new Sophie makes him bacon for breakfast, which the old Sophie didn’t like. At first, each thinks that the other is somehow making progress, becoming more cooperative, more committed to intimacy and rebuilding the relationship. But then it becomes clear that only one of them can enter the guest house at a time, and that the spouse they experience inside is someone new, different, and possibly some sort of projection, not a real person at all.

Ethan and Sophie respond very differently. He takes it on as an opportunity for rational detective work. “Of course you thought the fun was the investigation,” Sophie says, reminding him of the magic show where she enjoyed the show but he insisted on deconstructing all the tricks.

The original Sophie and Ethan at first decide to leave. It is just too creepy. But then they decide to return, making a pact about how each of them will handle the guest house doppelgangers. Is that the therapy? Giving them a shared experience so bizarre that it jolts them into working together to puzzle it out may be part of rebuilding their relationship, after all. “It’s like an exercise in trust,” Ethan says.

Screenwriter Justin Lader plays out the possibilities very cleverly, and it would be unfair to spoil it further. If the ending is not all one might hope, more of a trick than a conclusion, the performances and the ideas are provocative, fun, and something of a therapeutic trust exercise of their own.

Parents should know that this film includes very strong language, sexual references and situations, drinking, and drug use.

Family discussion: What is your explanation for how this retreat came together? If you had a chance to enter the guest house, would you? What would you find there?

If you like this, try: “Safety Not Guaranteed”