A few months ago, I traveled to a new city in a foreign country to talk about a book I’d written. At lunch one day, my host told me about a publishing acquaintance of hers who’d hosted the writer Rachel Cusk some years back, only to find herself seemingly replicated later, in cartoonish and (she felt) unflattering form, within one of the books in Cusk’s Outline trilogy. The woman was apparently devastated; although Cusk had withheld some details, the portrait, according to its presumptive subject, was specific and precise enough that anyone who knew her and read the book would immediately recognize the person being portrayed.“Every journalist who is not too stupid or too full of himself to notice what is going on knows that what he does is indefensible,” Janet Malcolm wrote in her classic 1990 book, The Journalist and the Murderer, about a nonfiction writer who used ethically questionable means to get close to a subject. Does the same theory hold true for autofiction? The license that art allows is generous, which Cusk has learned to make use of. On the occasions when she’s written openly autobiographical works, she’s been pilloried, or even sued: Her 2001 book about motherhood, A Life’s Work, was lambasted in the British press for its frank portrait of maternal self-abnegation, and her 2009 book The Last Supper sparked a libel lawsuit from a man who took issue with her depiction of him. (The publisher settled the suit and printed a revised version of the book.)But it was Cusk’s 2012 memoir about her divorce, Aftermath, and the excoriation she received for its exposure of supposed private family matters, that seemed to bring her to a breaking point. “Without wishing to sound melodramatic, it was creative death after Aftermath,” she told The Guardian two years after publication. “That was the end. I was heading into total silence—an interesting place to find yourself when you are quite developed as an artist.”[Read: The uncoupling]Instead of retreating, she turned that silence into its own ingenious form. Outline, published in 2014, is about a writer named Faye who’s traveling to Greece to teach creative writing, and its conceit is that Faye is an almost entirely passive vehicle for other people’s stories, which different characters spill out to her with unguarded enthusiasm. The book and two following installments, Transit and Kudos, were categorized as novels, which offered more protection than Cusk had previously been allowed. Still, Cusk made clear that what she was really interested in as a writer was truth—the resonance of pure reality. “I’m certain autobiography is increasingly the only form in all the arts,” she said in that same Guardian interview, which is an unusual thing to declare on a promotional tour for a work of ostensible fiction.Life of M, Cusk’s newest book, takes autofiction’s familiar dance of authorial ambiguity and shakes it into something odd and unsettling. “A little while ago I told the actor M that I was thinking of writing her autobiography,” it begins. M, as has been widely reported, is believed to be either based on or inspired by the actor Natalie Portman, who has praised Cusk’s writing and featured it in her book club. Both women live in Paris, where Life of M seems to be set. M is described as having first become famous as a child, and two of her roles—playing a ballerina and a performer who survives a school shooting—seem easily recognizable as Portman’s roles in Black Swan and Vox Lux. M, like Portman, is an avid reader, a mother, and a star of such renown that the world bends itself to accommodate her. When the narrator proposes writing about M to her, the actor initially likes the idea, asking wryly, “Would you just make it up?”For most of the book, like M, we’re left to wonder what the answer to that question is. Cusk has long blown up form and genre in her attempts to capture the authenticity of female experience. Her pursuit is relentless and uncompromising; it’s also bound by a logic that only Cusk herself seems to really understand. (You cannot write an autobiography of another person, any more than you can write a fictionalized portrait of one of the most recognizable women alive and expect most people to understand what about it is or isn’t true.) Life of M is a strange book, written with cold formality. But in its final pages, it performs an astonishing rug pull that makes you wonder whether the book actually has been an autobiography all along, interested in exposing not M but the knotty and unpalatable process of Cusk’s art.In the first pages of Life of M, the author meets M at a bookstore. We are told that M is “interested in books,” that she is small and her house is large, and that “her smile had a sweetness that almost seemed to reproach those who look at it for their dim and suspicious view of life.” The author finds it “hard not to feel ugly next to M”—the words ugly and ugliness appear almost 30 separate times over the book’s 180 or so pages—but seems drawn to the contours of their difference. M is portrayed as kind and thoughtful; the author comes across—intentionally, I am presuming—as surly and paranoid. “I had never learned how to make experience easier for myself,” she writes. “For M it was the reverse. Her difficulty lay in her distance from the random violence of insignificance.”After this short introductory section, we do not hear directly from the author again until the end of the book, when she goes to meet M to discuss what she’s written. The chapters in the middle toggle between scenes describing M’s life and more elliptical sections written in the first-person plural, which seem to interrogate experiences shared by the author and M. “We live in the same city but millions of other people live here too,” the first of those first-person-plural installments begins. That city is beautiful yet unstable, full of sidewalk cafés and cultural venues and tourists, but also of “angry people, people who shout and rail in the streets.” Cusk, in these sections, has the wafty portentousness of a stoned philosopher. “Often we don’t know what to do, how to occupy ourselves,” she writes. “Then at other times, we’re very busy and the idea of creating ourselves seems less important. But suddenly we find it is there, the question: Who are we? Yet everyone else seems to know who we are.”These interludes are, however, brief; the majority of the book comprises the descriptions of M engaged in the day-to-day business of her life: She reads Marcus Aurelius in a hotel room, she conducts research for a role by visiting an archive related to a historical figure, she meets a friend for coffee. Cusk begins many of these scenes with the same French-inflected sentence structure: “It is a hotel room in a foreign city.” “It is an office, square and high-ceilinged, with walls of paneled wood.” “It is the interior of a limousine. The air inside it is scentless and almost without temperature.”The descriptions sometimes go on for several pages, as though Cusk is writing stage directions or action lines in a screenplay. But inevitably, we end up in M’s inner thoughts. She struggles to relate to a friend’s depression. Returning home after an acting job, she feels strangely like she needs to get into character as herself. At a dinner party one night, as a pie is cut up and served at the communal table, she senses “a great chasm of loneliness and terror yawn inside her, as though this knife were intended for her. She would be split open and made to come out.”Some authorial projection here seems likely, given the precision with which Cusk describes M’s emotions, the “sensation of ground glass running in her veins instead of blood” when she has to meet with a man with whom she formerly had a relationship, who once “relished her fame” but now “sees it as a limitless series of opportunities for contempt.” But the descriptions of M sitting on a terrace above an olive grove, or meeting with her creative team, or participating in a book event sponsored by a fashion house feel distinctly real. They have the chilly detachment and careful texture of observation. They’re also laced with what feels like judgment: While reading on her terrace, M “lifts her eyes to the horizon with its primitive blue-grey shapes of islands washed in milky light, for the book is in French and does not entirely hold her attention.”Several times, Cusk refers to M as having projects: She makes a point of befriending interesting people, for instance, or tries to mentor “younger female actors” to help them “avoid some of her own errors and misconceptions.” What is Cusk’s project? Toward the end of the book, the author returns, showing M “some of what only I was referring to as our project. She didn’t seem to like it very much. She said we needed to talk.” The author goes to see M in her big house, taking care to describe the scrolled mantelpiece of the fireplace, the polished herringbone parquet of the floor. M doesn’t like how she’s been portrayed. “It’s hurtful,” she says. “But it isn’t you,” the author explains. “It isn’t anyone.”M points out that “she had never been to any of the places I described, nor done the things I had narrated.” The author struggles to communicate how none of that matters—that what she’s written isn’t a portrait of M but a rendering of the author’s own “private interior world” refracted through someone else. But all M can see are deficiencies—or, rather, the author’s projections of them—made real on the page. “You’ve made it seem like I lack humanity,” she says. “But you’re just playing a character,” the author replies. “The character was invented by me. So if that’s true, then it’s me it’s true of.”[Read: In defense of fakeness]Is Life of M about Portman, or Cusk, or neither, or both? Cusk’s “we” seems to seek out points of commonality between the two, despite their many differences: Both are well known, though to different degrees; both have seemingly difficult or tense relationships with their parents; both have had intimate relationships end under public scrutiny; both work in creative realms, although M insists that she is not a creator but “merely an element in the creations of others,” a statement that bears extra weight by the end of the book. And yet in its final pages, the author finds her power as a writer—the capricious and godlike influence of the storyteller—bludgeoned by M’s authority, her look of “mechanical power, a power that seemed to erase what it looked on.”That final scene is freighted with tension. M is cold and angry; she feels betrayed. She forbids the author from using her name. More significant, everything we’ve read in the book thus far (the descriptions, the interiority, the endless self-scrutiny) is seemingly revealed to be false. M is just one more person left offended by the author’s excavation of her. The author, for her part, doesn’t seem to care about the truth of who M is—“I haven’t even googled you,” she says—so much as how she can manipulate the idea of M to make sense of her own life. During a year when the author had been preoccupied with her partner’s grave illness, she says, her focus on M “had enabled me to leave and go and live in someone else.”To be a writer in this way is to be parasitic—to latch onto someone real and to try to draw out their life force to make art. It isn’t exactly defensible, but for Cusk to expose that practice is deeply fascinating, particularly in a book that some were always going to see as ethically fraught—and that many readers will be reading anyway in hopes of revelation and insight. Which is, Cusk might argue, the whole point of literature: that even, or especially, in its most uncomfortable form, it offers us moments of authentic humanity that thrum with recognition.“I don’t really believe in character,” Cusk once told the author Sheila Heti. “I believe in moments of truth.” There is, Heti said in response, “a darkness in how far away we are from truth, how all the forces in life sort of conspire to keep one away from it.” But there’s also a darkness in seeking to uncover it, especially when the truth at hand isn’t your own. I can’t decide whether Cusk’s willingness to delineate and accept this paradox in Life of M is admirably resolute or absolutely merciless. Or both.