PARK CITY - During the Q&A for Charlie McDaniel's "The One I Love," an audience member asked the director and cast how would anyone be able to market this film without giving its big secret away? McDaniel, stars Mark Duplass, Elisabeth Moss and screenwriter Justin Lader laughed it off, but the same question could also be asked of someone reviewing the film. How do you attempt to review a movie where part of its success is not knowing a major key ingredient to the story? Perhaps that's why the term "spoiler alert" was invented. In any case, we're going to give it the old college try. And, provide an out if you'd like to stay ignorant of the set-up because this is one movie with more surprises than you could ever imagine.

"The One I Love " begins somewhat conventionally. The audience is first introduced to Ethan (Duplass) and Sophie (Moss) as a married couple working through their troubles in therapy. Their counselor (Ted Danson), recognizing they are both out of synch more than they realize, suggests they take a weekend getaway at a private vacation home he knows of just north of Los Angeles. They take him up on the offer and soon arrive at a gorgeous, private and deserted estate in Ojai. Both Ethan and Sophie are overjoyed at the huge main house, the beautiful grounds and palatial pool. While exploring, Ethan notices there is also a cute guest house on the property. He quickly checks it out, it's empty, but neither of them think much of it. That first night is spent chatting over dinner sharing each other's company. They eat, they drink, smoke some pot and finally relax around each other for the first time in a long time.

At this point, "The One I Love" appears to be yet another conventional indie drama about a couple trying to reestablish the bonds of trust. Yes, it's a plot you've seen in at least a hundred other movies from around the world over the past 30 to 40 years. But, that's actually a red herring when the film's true subject matter is revealed.

[At this point, you are now being served with an official spoiler warning. If you do no want to know the twist that occurs about 20 minutes into the film, stop reading this review now. It's this author's belief it will be impossible for any studio who acquires the film to market it without giving this aspect of the plot away in some way.]

After dinner, Sophie decides to go and check the guest house. She's playing with a set of Russian Dolls when Ethan appears. Perhaps its the great dinner, or the pot or wine, but she lets her guard down and they start to connect again. Soon, they are having sex and joking like old times. Taking a quick break, she heads back up to the main house. She walks by a side room and is surprised to see Ethan sleeping on a couch. She wakes him, asking him how he got up from the guest house so quickly. Ethan has no idea what she's talking about. He passed out after dinner. Things turn ugly and Ethan is told to go sleep in the guest house.

Ethan complies and soon plops himself on the guest house sofa. Half asleep, he soon finds Sofia lying on him, cuddling up. All is forgiven pretty quickly, right? Ethan wakes up the next morning to the sound of Sofia cooking in the guest house kitchen, except she's cooking bacon for him. She hates bacon. This immediately makes no sense to Ethan. He returns to the main house to find Sofia there after he thought he'd just seen her in the guest house. Yes, something strange is going on and after a brief "let's get out of here" moment, both the "real" Ethan and Sofia quickly realize this strange gift could actually help their relationship. Of course, who these other "Ethan" and "Sophie" creatures are remains to be seen.

For a conventional review, that might seem like a tremendous amount of plot to give away, but for "The One I Love," trust that it does not. It sets up, however, the last 2/3rds of the picture, which turns into a roller coaster of more twists and turns. The film plays with genre, the audience's expectations and who they sympathize with most. It's a concept movie that really isn't a concept movie because at the end it's all about the relationship between Ethan and Sofia. Can their marriage be saved? Should it be?

The most impressive aspect of "The One I Love" is that while there was a plot line worked out beforehand, a majority of the scenes were improvised by Moss and Duplass on set or were quickly written the night before. The result is so succinct that if if you didn't know the production's creative process you'd think the movie was a much-heralded Black List script that some Hollywood studio was dumb enough to turn down. How something this smart and moving could be formed mostly from on-set improvisation is utterly remarkable.

As for the performances, it goes without saying that both Moss and Duplass are on their A game. Not only must they improvise as their original characters, but as a second set as well. Duplass in particular gives one of the best performances of his career as two very distinct Ethans.

McDaniel, a graduate of AFI and TV industry veteran, shows a very deft hand. In fact, this film will be a wonderful calling card for future studio work. That's not to say he doesn't have a home in the independent film world if he wants it, but his style is very commercial and you should see him attached to some studio comedy or romantic comedy soon. One of his best decisions was to bring on composers Danny Bensi and Saunder Jurriaans. The duo previously scored films such as "Simon Killer" and Denis Villeneuve's "Enemy." Here, they find a middle ground between an almost conventional score and their usual experimental tendencies. It works perfectly to set the tone for the picture and keep the audience on edge.

"The One I Love" is a picture that with the right distributor could be something of an art house sensation. Even if you don't find yourself laughing at all of the relationship humor, the mystery of what is really going on should captivate your attention. Nothing is what it seems until the film's final frame. And that's not something you can say about most films these days.