When they all meet in the dining room
In truth, this movie is really one giant OMG scene, because its very premise is presented as an unfolding series of surprising twists. Ethan (Mark Duplass) and Sophie (Elisabeth Moss) are a couple in crisis, and so their new therapist (Ted Danson) suggests they take a weekend at a getaway residence a couple hours out of town. It's a gorgeous, remote property with a pool, and, it turns out, a magical guest house where Ethan discovers a second, more permissive Sophie, and Sophie discovers a second, more agreeable Ethan. These mysterious copies of their spouses also can't leave the guest house, and Ethan and Sophie spend the film trading off exploring their time with their respective alter-spouses.
The twist that launches the film's final act, however, is a doozy: Just as Ethan's suspicions about Sophie falling for his copy are reaching a crisis point, they both enter the main house and find both their copies there, sitting at the dining room table, waiting for them. The old rules fly out the window, and the movie spins in even stranger directions.