KATHERINE BOO'S BEHIND THE BEAUTIFUL FOREVERS, set in a Mumbai slum, is a marvel of reporting, its triumphs legion. The characters are striking, vibrant, and dimensional, not at all the stereotyped, ghostly manifestations of ideas that too often plod through similar works. Boo’s players are unvarnished; they’re un-theorized and real. She records their stories clearly and candidly, tales which are profoundly compelling.

Boo writes in a genre called creative/narrative/literary nonfiction, an approach that blends the fact- and research-basis of traditional journalism with the storytelling devices of literature: setting, detailed description, and characterization. She began reporting in the late 1980s for the Washington City Paper. Her editor there, Jack Shafer, says that Boo “had the soul of a poet but the arm strength of an investigative reporter."

Boo moved on to the Washington Monthly and, shortly thereafter, to the Washington Post, where she turned out poignant pieces about the city’s underclass: poor single mothers, drug dealers, housing project denizens — people whose situations were less misunderstood (though they certainly were that) than unknown. One of Boo’s articles, from 1993, documents her time spent on the street with a crack-addicted prostitute, Starla, who has sex with men in order to amass each day the $60 she needs to get and stay high. It’s a scenario replete with traps for a reporter but Boo carefully avoids them, never wallowing in the more sordid details nor using Starla as mere backup for comment on rehab programs or the war on drugs. She tells Starla’s story with no identifiable motive other than to make the story known.

Boo’s preferred approach is to immerse herself in an environment, learning about its inhabitants by spending time with them. For years that environment was the rougher parts of Washington, D.C., but in Behind the Beautiful Forevers, her first book, it is Annawadi, a Mumbai slum of some 3,000 people across a “coconut-tree-lined thoroughfare” from the Chhatrapati Shivaji International Airport.

Annawadi’s first residents came to Mumbai in the early 1990s from the southern Indian state of Tamil Nadu, to repair a runway. They finished their project and then stayed, deciding that “a sodden, snake-filled bit of brushland” by the airport “seemed the least-bad place to live.” They cleared the brush and transferred dry dirt to the muddy morass, gradually rendering the area barely habitable.

Boo arrived in Annawadi sixteen years later, in November 2007, when she was touring Mumbai with a government official and a social worker who were squiring her from one location to another. At each stop, groups of women had been assembled to attest to the utility of government-run social programs. Last on this orchestrated tour was Annawadi, where Boo surveyed the crowd and noticed one woman, in particular, clearly uninterested in the proceedings. She was Asha, and she stood, aloof from the charade, next to a beautiful, younger woman — her daughter, Manju. Boo was struck by the pair and later told Outlook India that she “sensed there was another story there. How did Asha manage to raise such a daughter? […] What was the real story of these women?”

For the next three and a half years Boo reported in Annawadi. She was there early and stayed very late, lingering around the residents, talking to them, t...