Rachel Kushner’s new novel, “Creation Lake,” is set in rural France, but not the rural France of guidebooks and Peter Mayle memoirs. No one rhapsodizes over an escargot or a tarte Tatin. We’re in the country’s southwest, where the soil is rocky. More essentially, we are in what Kushner calls the proletarian “real Europe,” with vistas of “highways and nuclear power plants” and “windowless distribution warehouses.”

Kushner’s narrator is an American spy-for-hire. She’s 34, a dropout from a Berkeley Ph.D. program in rhetoric. She is working under an assumed name, “Sadie Smith,” that has unnecessary — for this reader — literary undertones. Sadie has come to this region to infiltrate a radical farming commune bent on violence.

Sadie is not, in the manner of a John le Carré character, longing to come in from the cold. She is already one of the coldest customers serious American fiction has seen in recent years. The isolation, the danger and the emotional hardships of her work (including unwelcome sex) roll off her shoulders. She likes what she does. She has a knack for it.

Biographical details about Sadie are scant, though the reader is made aware of two of her previous assignments. At 24 she infiltrated the Gypsy Jokers motorcycle gang, where she was the “old lady” of an older biker she put in prison. Later she convinced a troubled young man to buy 500 pounds of fertilizer for bomb making. When he was found innocent at trial due to entrapment, she was fired by the FBI and went freelance.

I dislike plot description because it’s close to meaningless — everything I’ve said so far could apply to a bland Hulu drama series as well as to a sinuous and powerfully understated novel, which “Creation Lake” is — but here is a necessary bit more.

The farming commune is called Le Moulin. Sadie is well-read in the history of radical movements, but as she befriends the group’s key members, she imbibes their philosophies and absorbs the revisionist ideas that have been passed, like batons, down generations. The leader, Pascal, is a womanizer and a self-styled heir to the French Marxist theorist Guy Debord.

Pascal’s own mentor, a man named Bruno, is a veteran of the May 1968 protests in Paris. He knew Debord. Bruno long ago drifted to the countryside, sensing that his generation’s best efforts had come to less than nought. He now lives literally underground, in a cave system, partly for reasons of personal grief. He is a near-mythical figure. Bruno sends cosmic and cryptic emails, which Sadie intercepts, about Neanderthal consciousness and why what remains of their DNA in many of us matters. These are more interesting than they sound.

Sadie works for the money — that is, her unknown employers appear to be the agricultural conglomerates who want to see the commune’s members in prison. One of this novel’s most unnerving aspects is listening in with Sadie on so much ardent talk about social rebellion, while knowing she doesn’t care — she intends to betray these people and disappear. Her ambiguities are not those of the divided soul.

Kushner was born in Eugene, Ore., and she grew up there and in San Francisco. Her writing has a Western roominess. She’s the author of three previous novels, most notably “The Flamethrowers” (2013), which is about art, motorcycles and violent Italian politics, and “The Mars Room” (2018), about a woman imprisoned for life for killing the man who stalked her. “The Flamethrowers” has more flair, more intensities — but both novels are bold and intellectually alive.

“Creation Lake” is a step up from both, and it consolidates Kushner’s status as one of finest novelists working in the English language. You know from this book’s opening paragraphs that you are in the hands of a major writer, one who processes experience on a deep level. Kushner has a gift for almost effortless intellectual penetration.

She moves easily from the abstract to the concrete, and her themes overlap and bleed into one another without seeming forced. Here’s one example, a scene I will never forget. In a flashback we learn about a boy who played in the French woods near the end of World War II, after the Nazis had fled the area. He found the helmet of a dead German soldier and put it on his head.

To his horror, he discovered he had inherited the dead man’s lice. They ran riot on his head; it was awful. They were unstoppable until they’d eaten everything they could and departed in search of a new host. The kerosene used in failed attempts to eliminate them caused permanent damage to his eyesight.

This young man was Bruno, the now-aging radical. His parents had sent him and his sister to the country from Paris as Nazi troops advanced. The siblings will not discover until later that their mother died at Buchenwald and their father in the Nazi-run Fresnes prison in France. For Bruno, the lice have become a metaphor, not just for the dispersal of ideas but “for the transmigration of life, from one being to the next, from past to future.”

Kushner writes about shoplifting, about comb-overs, about French novels versus American ones, about the smell of hay, about the feeling of riding in a backwards-facing seat on a fast train, about graffiti (“Murder is understandable when you think about it. … But to spray paint an inscrutable sloppy symbol on the outside of a building? Why?”), about how politics affects dress, about social class, about fires, about “fake tough girls” at Berkeley who bend their fingers in insistent air quotes, about cinephiles and about the height at which old French men wear their belts. She takes a floor-level interest in humanity. Close observation of this sort never grows tedious.

At bottom, “Creation Lake” is about character; Kushner’s interest in it runs as deep as Hemingway’s. Character is more important to Sadie than politics. She may be ready to inform on anyone, for now, but she most dislikes those humans who are tamed cats with clipped claws.

Has ecological terrorism grown tired as a fictional subject? Probably. Might this novel’s ending have landed a bit harder? Perhaps. These are topics for further discussion. For now, it’s enough — for me, at any rate — to stand in the hard rain this novel generates.