Ever since Ursula K. Le Guin and Edward Abbey lit the fuse back in the 1970s, there's been an ever-growing explosion of political eco-fiction. From Octavia Butler and Richard Powers to Amitav Ghosh and Margaret Atwood, novelists have gotten more and more fascinated with those who fight to save the environment.

One such group occupies the center of Birnam Wood, the whooshingly enjoyable new novel by Eleanor Catton, a New Zealander whose previous book, The Luminaries, made her, at 28, still the youngest person ever to win the Booker Prize. Where that 2013 novel was a wild-and-woolly beast, Birnam Wood — its title comes from Macbeth — is shapelier and more conventional. Filled with utopian hopes, personal betrayals, accidental deaths and profoundly unaccidental murders, this New Zealand-set book is a witty literary thriller about the collision between eco-idealism and staggering wealth.

The story begins by introducing three 20-something members of Birnam Wood, a guerrilla collective that seeks to fight capitalism and ecological devastation by, legally or not, growing things on unplanted land, public and private. There's Mira, the group's willful and charismatic founder. There's her burnt-out sidekick, Shelley, who does the grunt work and secretly wants to quit the group. And then there's Tony, the most radical thinker of the bunch who has returned to the group after several years abroad. He has romantic hopes for himself and Mira — hopes that Shelley quietly hopes to sink.

Mira hears about an unoccupied farm owned by Sir Owen Darvish and his wife Jill, who embody the solidity and complacency of well-off Kiwis. Mira thinks it perfect for a Birnam Wood project. But when she drives there from Christchurch, she discovers that it's been bought by Robert Lemoine, an elusive American billionaire/drone manufacturer who says he plans to build a survivalist bunker. Attracted to Mira, Lemoine offers to help finance Birnam Wood. Because her group badly needs money, she's interested. But will a rich benefactor's money help the group spread its message — or corrupt it?

While Catton has sympathy for the grand idealism of the Birnam Wood collective, she also sees its fault lines. Indeed, the book's at its best taking us inside the characters' heads to lay bare the illusions, desires and petty motivations that often work against their dreams. For instance, Mira emerges as something of a modern-day version of Jane Austen's Emma — Catton actually scripted a 2020 film adaptation of that novel. Mira's sense of political righteousness blinds her to her own motivations. The disaffected Shelley accuses her of "rebelling for the sake of it, like she had always done, acting as though the rules that bound the little people were just too tiresome and ordinary to apply to her."

Working in the tradition of the 19th-century novel — one hears echoes of George Eliot as well as Austen — Catton likes to confront her characters with choices and then lay bare the consequences, often unintended, of what they've chosen. There's a great, lacerating scene in which Tony, a world-class mansplainer, falls out of favor with the group by attacking identity politics and intersectionality. Because of this split, he will wind up spying on Lemoine — a move that sends the plot caroming in a wild new direction.

You see, while our heroes in the collective are muddling their way through ordinary human issues, they're faced with a villain from a 21st-century thriller. Lemoine isn't merely an amoral billionaire with all the compassion of one of his drones. He's a high-tech bad guy, complete with NSA-level spyware and mercenaries to do his bidding. Too bad to be true, he's so skillful at wielding his malignancy that, in spite of herself, Catton seems to hold him in a kind of awe.

Normally, it would be an artistic flaw that realistic characters like Mira, Shelley, Tony and the Darvishes must confront such a comic-book baddie, and I guess it is here: What starts off looking like a novel about character winds up in a climax out of a genre novel. Yet the story plays like gangbusters: I devoured all 400-plus pages in two days.

And in showing the collective's encounter with Lemoine, Catton taps into a feeling very much of our moment. We live at a time when many environmentalists feel helpless next to mega-rich forces who seem able to despoil the planet as they wish and to avoid any governmental attempts to check them. In Birnam Wood, we see the consequences of this gap in power, and the results are not pretty.