The dust jacket of J.K. Rowling's ballyhooed new book, The Casual Vacancy, available today, bills it as "her first novel for adults." It's Rowling's first published work since she wrapped the mega-selling, seven-volume Harry Potter fantasy saga in 2007. And that puts her, and The Casual Vacancy, in a uniquely awkward position. The public knows Rowling as a fantasy-fiction Pied Piper; in an age ruled by videogames, her books got kids—even kids who otherwise don't read much—to thrill over every gripping chapter in a 4,100-page adventure saga about plucky young wizards vanquishing evil. By the series' end, the books had become grown-up enough in tone (they matured as the kids in the story did) that nobody now thinks of them as overtly childish. Plenty of adults love the Potter books.

But that general-audience suitability goes out the window with The Casual Vacancy. The "for adults" tag isn't just a declaration of high literary purpose. It's a warning that this 503-page portrait of vicious, rich-versus-poor politics in the fictional English village of Pagford is in no way, shape, or form a bedtime story. Thanks to a crime-plagued, addiction-riddled public housing tract on the edge of town, Pagford's citizens are haunted by questions of whose obligation it is to cope with the crushing poverty and substance abuse of their less-fortunate neighbors. In some ways, it's an English version of Desperate Housewives, a study of suburban malaise. But Wisteria Lane feels like Walton's Mountain compared to Pagford. Are Rowling’s adult fans ready for this rough a ride?

There are plenty of pleasures to be had in The Casual Vacancy for those who like their social satire on the savage side. If you enjoyed the way Rowling skewered infuriating characters like, say, the officious bureaucrat Dolores Umbridge in the later Potter books, you may also groove on her merciless vivisection of pretension, hypocrisy, and venal behaviors of all sorts in both adults and teens. The hyper-intricate plot turnings involve, among other things, a verbally and physically abusive father prone to terrifying rages, and a horrific rape scene dispatched with chilling matter-of-factness. Parts of the story would be tonally of a piece with any Richard Price or Dennis Lehane novel, or an episode of The Wire. A sense of alternating rage and despair pervades many passages, both within the characters and in the book’s larger narrative arcs. Is Rowling in a sort of delayed fury at what she saw during her own years on public assistance as a single-mom divorcee in the 1990s? It certainly seems so. She's burning with a sense of social outrage.

On that score, she’s got her finger firmly on a hot-button issue. The central conflicts in The Casual Vacancy all turn on the sudden death of a local crusader devoted to helping the impoverished. His demise brings to a boil a decades-long grudge match over who should care for the less fortunate in town, and how much should be spent on them. There are many arguments over “responsibility” in the novel, and some of the positions taken by conservative characters sound remarkably like Mitt Romney’s now-viral comments about America’s 47 percent.

But Rowling’s escalating alarm over how the underprivileged in society are treated grows strident at times. If being "adult" means pushing much harder on life's ugliness than she did in a fantasy milieu, maybe that's a mixed artistic blessing. And as The Casual Vacancy unfolds like a roll of ever-sharper barbed wire, it's hard not to think that Rowling has perhaps satisfied herself and her passions more than she'll satisfy readers. She may also find she has a lot of pissed-off parents on her hands, concerned that she's put so much teenage drama—the biggest plot explosions turn on adolescents posting nasty messages online—in a story too graphic for the many tweens likely to be intrigued by it. (She remains as good as ever at crafting believable and moving interior monologues in the anxious heads of sullen, troubled children.)

Rowling has said that she has never presented herself as a do-gooding "babysitter" or "teacher" for child readers. She's right to defend her Potter books as honest and adult in their own way. But The Casual Vacancy isn't just unblinking about the sordid side of life. It's almost gleefully clinical in cataloguing the worst impulses of humankind, and at bringing us into the heads of bigoted, vituperative locals ruled by tradition, spite, and envy. It's Dickensian in its contempt for corrupt people and institutions, and it comes on like narrative napalm. Prepare to be singed.