One of my top picks from SIFF last spring, this movie comes swaddled in spoilers. It’s almost impossible to describe the fanciful sci-fi plot without resorting to significant clues. Oh, it’s like a certain TV show from the early ’60s or that novel by Dostoyevsky. (Here’s my precis: Two Edward Albee characters trapped in an enchanted Williams-Sonoma catalog.) Better, then, that we be vague about things.

Sophie (Elisabeth Moss) and Ethan (Mark Duplass) are a bickering L.A. couple making no progress in marriage counseling. (Ethan’s affair will be revealed later.) Childless and confortable, they’re studies in yuppie self-absorption, neither one willing to concede ground to the other. They’ve hardened into roles—almost caricatures—of their younger, more loving selves. Their smooth therapist, never named, has his every suggestion rebuffed; so maybe it’s time for a new approach, he says. There’s a weekend retreat that’s worked well for other clients—and he hands them the keys. (Later, we’ll think back to that serenely self-confident therapist, played with not-quite-malevolent opacity by none other than Ted Danson.)

At the retreat is an iPad with gushing testimonials from past guests. They all profess to be thrilled and grateful for the experience. (Remember them, too.) Sophie and Ethan are more skeptical as they rehash their past. What became of their fun, Lollapalooza-going, X-dropping days? What happened to their kinder, cooler selves? Anyone who’s been in a long-term relationship or marriage will know the same feeling of past/present discontent, which writer Justin Lader and director Charlie McDowell cleverly filter through a refracting lens. (Duplass actually gave them the movie’s premise to develop.)

Interrupted from their idyll by what Ethan calls “the weird people,” our duo first decides to flee. Then Sophie says they should “explore it further”—maybe like one of those youthful druggy weekends when anything could happen and reality was called into question. Over this very strange and peculiar weekend, Moss and Duplass get a real actors’ workout. Watching them, you need to be attuned to hair and wardrobe changes, her makeup and his eyeglasses. Ethan and Sophie must track these shifting nuances, too. Just how well do you know your spouse? You want to be a better partner, but it takes so much damn effort. And The One I Love forces Ethan and Sophie to make that effort; their very freedom depends upon it. Thus their weekend lesson may be this: A successful relationship requires you to be a very good actor. Opens Fri., Aug. 22 at Sundance Cinemas. Rated R. 91 minutes.

bmiller@seattleweekly.com