The shadowy final shot of Nora’s face in “G’Day, Melbourne” as water sluices over her is a masterful, flickering button on an episode that emphasizes interpretation — the gulf between seeing and understanding, or what can be observed and what’s real. “The Leftovers” frequently offers its viewers an allegory that can be interpreted in multiple ways, and this final image rests in that same vein. Nora’s downturned face has a Madonna-like quality to it. Meanwhile A-ha’s “Take on Me” plays peppily in the background, a song that despite its synthesizers has rather melancholy, abstruse lyrics. In the song’s famous music video, two lovers escape mysterious attackers, jumping in and out of the pages of the book. In “G’Day Melbourne,” Nora and Kevin have what might be their final conversation on this earth while setting a mysteriously powerful book on fire. As usual, “The Leftovers” finds a way to mix the sacred with the profane, the secular with the theological, the real with the mythical.

There’s more tension between real and not-real in “G’Day Melbourne” than in any of the other “The Leftovers” episodes this season, primarily because Laurie, back in Texas, introduces the notion that Kevin is once again having a psychotic break. That Kevin’s experience might be both disordered and revelatory is one that the show has played with for a long time, but four episodes from the series finale (and several years, in the show’s timeline, since “International Assassin”), revisiting it feels poignant. Kevin is even once again in an incomprehensible hotel, interpreting messages through the television, before he runs through a maze of graffiti-covered walls to pursue a memory/vision/ghost/hallucination. It struck me that Kevin ends up going to the city library for answers — asking for a book called “The Assassins,” in another cheeky nod to “International Assassin” — as if, at this point, mere information would be able to solve any of his problems. It’s only when Laurie coaches him that he’s able to see who his quarry really is; believing is seeing, not the other way around.

“G’Day Melbourne” starts back in America with Kevin realizing that Nora is smuggling something through security. The fact that this secret is so casually acknowledged feels like the first sign that this is the beginning of the end for Nora and Kevin, even as they lock the door of the bathroom to have sex on the baby-changing table. It’s like they’re caught in a loop that keeps them both relatively functional but also apparently unfulfilled; there’s attraction and comfort, but so little communication, so little forward motion towards anything. Their relationship is encapsulated so well in that opening sex scene, which plays their mundane conversation over escalating lovemaking. Nora and Kevin seem to have sex to avoid having real conversations.

While Kevin seeks who he thinks his Evie, Nora seeks what she thinks is redemption — going to a mostly abandoned warehouse to see if the mysterious scientists will allow her to pass through. It’s hard to interpret what happens there (although always nice to see Katja Herbers); Nora is asked to submit to a medical exam that includes laying on a bed of Styrofoam peanuts in a closed wooden crate. She appears to pass with flying colors, but is then stymied by a question that appears to have already plagued someone else this season — the wandering stranger who sets himself on fire in the flats as Kevin Garvey, Sr. watches, in “Crazy Whitefella Thinking.”

“G’Day Melbourne” presents the two bickering doctors like they are gatekeepers in a Beckett play — engaged in a nonsensical conversation, sometimes one that is literally unintelligible because it is in a different language, about trivialities that happen to have the power to decide Nora’s fate. The question is: If you have the wherewithal to kill a baby, its identical twin will grow up to cure cancer. It will be a quick and painless death of someone else’s baby, and you don’t have to do it. But you do have to nod. The man in the flats said that he wouldn’t kill the baby; Nora says she would. Neither is answer is accepted by the scientists. Nora calls bullshit on the sudden heel-turn, naturally, only to be told that she should not bother. The team of scientists has an inscrutable, omnipotent knowledge — they know about Kevin, they knew about Nora’s disappeared children, and at least one of the scientists guessed that she was never going to do it, no matter how tough she sounded about it. But it’s never explained how or why they know any of that stuff — or why they would have a series of tests to evaluate who gets to go where the disappeared went, instead of just taking their money and sending them on their way. It’s kind of like Nora went to see the Sphinx — and is presented with a moral dilemma that has riled up generations of high school ethics classes. Apparently there was a right answer to the question, but it’s neither “yes, do it” or “no, don’t.”

This sets the stage for the final eight minutes of the episode, where Kevin finally calls Nora out. “That’s what we do. We don’t f–king talk about anything.” Carrie Coon, Justin Theroux, and director Daniel Sackheim are at the top of their game here, playing out a relationship-ending scene with self-loathing, horrified finality. The room is literally burning down around them — fueled by the pages of Kevin’s mythos, lit by the lighter Nora used for her secret habit. I wasn’t expecting “The Leftovers” to offer up a breakup scene — it’s more direct than I expect of the show — but it is so fitting that it would be punctuated by elemental rage. You can see the firelight flickering on Nora’s face as she confronts Kevin. And in the final moment, the water pouring down her face looks like eternal tears streaming from her eyes, as if she is mourning the entire weight of the world.

Correction, 7:52 p.m. PT: An earlier version of this recap misidentified the director of this episode. It is Daniel Sackheim, not Mimi Leder.