Nancy Doak walks her service dog, Tolkien, through a Home Depot in Crystal River, Fla. (Matthew Beck/Citris County Chronicle via AP)

Kerry Lauerman is The Washington Post’s national projects editor.

What type of animal stories captivate us more than just about any other? A few hints:

“Tiny Dog Rescues Girl from Attempted Abduction” (Yahoo News). “Dog Finds a Tiny Kitten, Risks Everything to Save Her” (Fox News). “3-Year-Old Siberian Girl Discovered after 11 Days Lost in Wilderness When Her Trusty Dog Summons Rescuers” (Siberian Times). “Heroic Senior Dog Saves Her Family from Charging Moose” (Boulder County News). “Hero Pit Bull Shows Up Lassie, Uses iPhone to Call 911 and Save Owner’s Life” (Huffington Post).

Dog-as-hero tops all other stories about the animal kingdom, and the sampling above, culled by Melissa Fay Greene for her new book, probably resembles a lot of what’s clogging your social media feeds. But in “The Underdogs,” Greene gives us a selection of deftly reported and illuminatingly researched stories that go much deeper than sentimental click bait, documenting the powerful ways dogs are helping reach some of the most vulnerable among us: children with disabilities.

Expanding on a popular New York Times Magazine story she wrote in 2012, Greene in “The Underdogs” focuses on the work done by 4 Paws for Ability, an academy based in Xenia, Ohio, that trains and places service dogs in extreme circumstances. 4 Paws was founded by Karen Shirk who, as a college student in 1989, received a diagnosis of a rare neuromuscular disease that left her on a respirator, unable to care for herself, and suicidal. When the established agencies that issued service dogs told her she was too infirm for one, she got a black German shepherd puppy she named Ben and trained him herself.

“I didn’t leap back into life with Ben so much as inch back into it,” Shirk tells Greene. She soon founded 4 Paws, and since 1998 has placed more than 1,000 of the group’s dogs.

Other than Shirk’s, the stories Greene tells in “The Underdogs” are of children with seismic difficulties — a tracheal tube and ventilator, severe forms of autism, fetal alcohol syndrome — and the 4 Paws dogs they are paired with at request of parents desperate to try anything, including an expertly trained dog for about $13,000, to give their children a taste of childhood.

One eager couple from Alabama took the gamble for Lucy, their adopted child from China, who has attachment disorder and post-traumatic stress disorder. An 8-year-old ruled by fear, Lucy is prone to screaming meltdowns, and remains convinced that her parents may well abandon her the moment she lets down her guard.

“It was as if Lucy were a colander and love, the bright water running through it, pooling for a moment before leaking and splashing away,” Greene writes.

Enter a fun-loving yellow Lab named Jolly. It’s no meet-cute story. Lucy worries that the dog will reject her or possibly even draw away her parents’ attention. Jolly becomes a threat, and for her, a screaming child is probably something to avoid.

But under required training from 4 Paws, the families learn strategies to ensure that the dogs and children bond, even if it requires careful manipulation. “You want the dog to feel: I don’t know what it is about this kid, but whenever this kid is around, good things happen,” a trainer tells Lucy’s parents. It starts with planting treats around Lucy for the dog, and progresses to giving treats to Jolly so she doesn’t run away when the child inevitably has a tantrum. But training the dog to accept behavior she’s meant to prevent can backfire. Instead of trying to calm Lucy down, Jolly could learn to look forward to her emotional breakdowns because they will lead to a treat. (“I don’t know what it is about this kid, but when she goes ballistic, good things happen!”)

Through persistence, the parents (who are the book’s other heroes) manage to forge the right relationship between the dog and child. In Lucy’s case, Jolly eventually became the calming, trusting source of strength her parents had hoped for, and a combustible child seemed to finally, remarkably, feel secure.

In another story, Connor is hobbled by a tracheal tube and a ventilator, a boy who “couldn’t explore on his own farther than the eighteen inches his tubing allowed.” At ate 7, he weighed just over 20 pounds and functioned more like a 4-year-old. When he began to withdraw from life rapidly and mysteriously, his parents brought in Casey, a goldendoodle, to help their son better engage with the world.

But when Connor suddenly disappears to the hospital, Casey is the one who becomes anxious and withdrawn. A working dog, this makes sense; he’s suddenly unemployed, robbed of a mission and a sense of purpose (and accompanying rewards). But he also exhibits undeniably human-like grieving behavior.

These are riveting stories not just because Greene, a master of narrative, picked good ones, but because she explains just how these relationships work at both ends of the leash. It’s not all feel-good Facebook fodder — there is one particularly unsparing tale of utter heartbreak here — but they’re important and revelatory stories. Greene invites us not to just marvel at the hero dogs, but understand them a little better, too.

Kim Kavin tells a starkly different story in “The Dog Merchants,” a sprawling, and sometimes fascinating, look at a complex industry. Her reporting reveals that by simply finding a dog to take home, we are dipping into a world largely veiled to the consumer and in many ways ethically dubious. Kavin travels the country visiting high-end dog shows, back-yard hobby breeders, luxe retail rescues and even the Hunte Corp., “the biggest legal distributor of puppies to pet stores across America,” which moves about 45,000 puppies a year.

In the most revealing chapter, she visits an auction in Wheaton, Mo., ground zero in the dog trade, where various breeds will be bid on throughout the day by a wide variety of dog merchants, from amateurs to those who will supply pet chains nationwide. One 18-month-old Yorkshire terrier, which already had given birth to at least one litter of puppies, goes for “$1,150, having earned a reputation as a good producer from a nice, young age.” Meanwhile, a trembling Chesapeake Bay retriever named Feldmann’s Big Boy, startled by suddenly standing in front of such a large crowd, was “so terrified . . . that he wrapped all four of his legs around the two handlers.” No one will bid even $1.

One helpful participant explains to Kavin how lucrative an already pregnant West Highland white Terrier that sells for $650 can be: “A commercial dog breeder will get two litters of puppies out of that Westie during each of the five years after purchase. Every litter with a Westie is four to eight pups. That means a total of eight to sixteen puppies a year, or forty to eighty dogs coming out of that single Westie in five years’ time.” After the eventual sales to pet stores, which ultimately sell the puppies for much more, that one $650 dog can generate up to $64,000 in sales.

All of this, of course, alarms those concerned about animal welfare, and who wish the demand for the latest hot breed could instead be met by some of the millions of dogs euthanized in dog pounds and shelters across the country. Which leads, though, to Kavin’s startling discovery that rescue groups also frequent the auctions, usually trying to save specific breeds from a grim life fueling the puppy industry. Of course, by bidding on these dogs, they’re also fueling the very demand they abhor.

Is this that big of a problem? Kavin can’t quantify just how often it happens and whether many of these dogs end up routed into rescues, adopted by the very people who have gone out of their way to avoid the dog-breeding industry. Is it just the occasional Jane Rosenthal, whom Kavin profiles, bidding away on Japanese Chins for her small organization Luv A Chin Rescue? Without more than anecdotal evidence, one would think so.

But Kavin is doing her part. With the release of the book, she’s starting a website of the same name that will let consumers register and post reviews of any breeder or rescue group, sort of a Yelp for dog buyers. If it shines some light on the shadowy, largely unregulated dog industry, I’d say that’s worth five stars.

The Underdogs
Children, Dogs, and the Power of Unconditional Love

By Melissa Fay Greene

Ecco. 344 pp. $27.99

The Dog Merchants
Inside the Big Business of Breeders, Pet Stores, and Rescuers

By Kim Kavin

Pegasus. 303 pp. $27.95