Sometimes, voice is all.

The physical attributes of Nick Carraway, Ralph Ellison’s Invisible Man and Scout Finch are barely outlined by their creators; instead, it’s their singular voices that give these characters their life and complexity.

So it is with Jai, a 9-year-old Indian boy who’s the narrator and main character of Deepa Anappara’s extraordinary debut novel, “Djinn Patrol on the Purple Line.” Jai lives in a basti, a sprawling slum located within an unnamed city in India. The home he shares with his parents and older sister consists of one room covered by a tin roof dotted by holes; it’s situated in the shadows of “hi-fi” luxury apartment buildings with “fancy names like Palm Springs and Mayfair and Golden Gate and Athena” where Jai’s mother and other women from the basti work as nannies and house-cleaners. The most expensive possession in Jai’s home is a TV, which he prizes because he’s an avid fan of reality police shows. As Jai tells us in his cocky, funny, sweet, gullible and altogether distinctive voice:

“My favorite shows are ones that Ma says I’m not old enough to watch, like Police Patrol and Live Crime. Sometimes Ma switches off the TV right in the middle of a murder because she says it’s too sick-making. But sometimes she leaves it on because she likes guessing who the evil people are and telling me how the policemen are sons-of-owls for never spotting criminals as fast as she can.”

In the opening pages of this novel, Jai is presented with a macabre opportunity to practice what he calls his “detectiving” skills when a classmate named Bahadur vanishes. Rallying to his side are a pair of juvenile Dr. Watsons: Pari, a Hermione Granger-type smarty pants and Faiz, who hails from a minority Muslim family and is especially fearful of Djinns, spirits made of smokeless fire. Jai introduces these companions by telling us readers, “They are my friends and they can see the thoughts in my head.” That’s as good a definition of friendship as any.

Week by week, more children and teenagers are snatched from the basti. Panicked residents, frustrated that the police are doing little about this epidemic of kidnappings because the victims come from poor families, begin to turn on each other. Muslims, like Faiz and his family, become targets of violence; eventually, so, too, do those “hi-fi” people, perched above the basti in their glittering towers. It’s up to Jai and his friends (or so Jai confidently thinks) to find the evildoers. To do so, the trio roam the crowded Bhoot Bazaar and dive into narrow alleys where goats, clothed in old sweaters against the winter chill, have covered the ground with their droppings. Jai even steals the ticket fare for Pari and himself to board the Purple Line train to search for Bahadur in the city center, even though neither child has ever gone so far from home on their own. Shrouding all these expeditions is an urban smog that, in the manner of Sherlock Holmes’s London fog, obscures the truth.

Anappara began her career as a journalist in her native India, writing about the lives of children growing up in poverty. In an interview appended to the back of “Djinn Patrol on the Purple Line,” Anappara says that, by some estimates, “as many as 180 children are said to go missing in India every day.” Disturbed by the way the lurid details of the crimes (including human trafficking and organ peddling) overshadow their young victims, Anappara wanted to return the attention to the children themselves, as well as their “resilience, cheerfulness, and swagger.” True to her desire to give voice to the most vulnerable, Anappara intersperses victims’ accounts, told from their own perspective, within the main narrative.

The moving and unpredictable novel Anappara wrote defies easy classification. Given the sometimes capricious exploits of its young investigators, “Djinn Patrol on the Purple Line” could conceivably be shelved in the YA section of libraries and bookstores. Anappara also plays in a self-aware manner with the narrative structure: chapter headings, for instance, consist of cheeky sentence fragments, such as: “THREE WEEKS AGO I WAS ONLY A SCHOOLKID BUT— .” Yet, the tale darkens into urban noir as it reaches its awful conclusion. By story’s end, Jai has grown more hesitant, humbled by tragedy and evils beyond his once-childish imaginings. Even so, his remarkable voice retains a stubborn lightness, a will to believe in the possibility of deliverance in this fallen world.

As another great (and older and more cynical) fictional narrator once said, “Isn’t it pretty to think so?”

Maureen Corrigan, who teaches literature at Georgetown University, is the book critic of NPR’s Fresh Air.

DJINN PATROL ON THE PURPLE LINE

By Deepa Anappara

Random House. 347 pp. $27