Editor’s note: In her book The Dog Merchants, writer Kim Kavin reveals the complex network behind the $11 billion-a-year business of selling dogs. She takes an investigative approach and meets breeders and rescuers at all levels, shedding much-needed light on an industry that most people don’t even realize is an industry. The following excerpt has been adapted from her book, which publishes May 2.

Michael Stolkey takes a measured breath before holding open the heavy, thick door that precious few outsiders ever get to walk through. “This is why people hate us,” he says, taking a few strides into the hallway on the other side. “The kennels.”

Stolkey is director of corporate sales for the Hunte Corporation, a privately owned business in Goodman, Missouri, that is at best wary, and at worst paranoid, about letting newcomers inside. The company, which opened in 1991, is likely the biggest legal distributor of puppies to pet stores across America, and it has long operated with great secrecy, hunkering down against the cries of animal-welfare activists and allowing only carefully prescreened visitors to pass beyond this threshold.

The business of readying puppies for transport to stores is conducted here in a well-honed, legally regulated, and systematic way, and the company’s sheer size, along with its supply chain of commercial and other breeders, are the stuff of great speculation and contempt. No conveyor belts or robot arms are at work, but even Henry Ford would be impressed with the assembly-line nature of operations. It’s one of the things that make Hunte a big, easy-to-loathe target. Animal-welfare activists have, among other things, followed the company’s trucks into the field and locked their drivers inside with the puppies, likely screaming from the asphalt about how the humans deserve to be trapped inside a cage alongside the dogs they’re selling in mass-production style.

On this day in late August 2014, routine operations were busy, but not hectic, thanks to the seasonal lull in puppy sales. The doorway opened into a brightly lit, white hallway so long that it seemed almost to disappear into the distance of the $10 million, at least 200,000-square-foot facility, in much the same way hallways in large, sterile hospitals vanish into a labyrinth of the unknown. Workers wearing different colored scrubs to indicate their job titles—veterinarian, technician, assistant—walked calmly to and fro, some with empty hands and others carrying one puppy at a time, petting them and cradling them as any dog lover might. A Siberian Husky pup, a baby Boxer, and a Shar-Pei with hair still growing into his face folds were among those being ferried back and forth to the photography room, the grooming room, and the surgery suite, giving the place an atmosphere similar to a large nursery filled with cuteness and coos.

One or two people have managed to sneak undercover cameras into the kennel section over the years, and YouTube videos show a bit of what goes on outside the public eye, where 13 numbered doors line the long corridor’s right side. Inside each one are rows of kennel-style cages like the ones in veterinarians’ offices and animal shelters. Some are large and some are small, to meet US Department of Agriculture regulations depending on each puppy’s height and weight. Two levels of the enclosures are on either side of every room, with the levels separated by a stainless-steel catch basin that is easy to clean after urine and feces falls through the metal-grate floors. Each room is climate-controlled and separately ventilated to prevent the spread of airborne diseases, and each appears to contain about a hundred of the enclosures.

At the height of operations before the 2007 global recession, the industry giant was buying about 90,000 puppies a year from breeders and distributing them to Petland and other retail stores, driving annual revenues to $26 million. Since the crash, Hunte’s business has been halved. Today it moves about 45,000 puppies a year, which likely means it is still the biggest distributor in America, the world’s biggest market for dogs.

The purchasing of the pups happens on Tuesdays, which are known as “buy day.” Hunte officials say they acquire puppies from USDA-regulated commercial breeders along with hobby breeders from Missouri, Arkansas, Kansas, Iowa, North Dakota, South Dakota, Indiana, Illinois, and Nebraska. Hunte agents fan out in climate-controlled vehicles outfitted with a scaled-down version of the kennel ventilation and enclosure systems, and they drive hundreds of miles each week, going door to door and offering breeders wholesale prices for their puppies along with the kenneling systems and supplies that are part of Hunte’s vertical business model. The agents are in the field Friday through Sunday, and they’re back in Goodman with truckloads of puppies by Monday night, in time for “buy day” on Tuesday morning.

Some of the dogs are purebreds with registration papers from the American Kennel Club, America’s Pet Registry Inc., or American Canine Association—founder Andrew Hunte once told AKC officials his company is the kennel club’s biggest customer in moving dogs that buyers later register with AKC for a fee—while other puppies are designer cross-breeds, like Goldendoodles, that regularly prove popular with retail consumers. The owners of pet stores nationwide send Hunte their wish lists, and Hunte tries to fill them through its network of breeders.

The minimum-age puppy Hunte says it will accept is eight weeks, and no dogs are accepted who weigh less than a pound and a half—because the company has learned that the ultra-small puppies usually lack an immune system developed enough to survive the move through the system into pet stores. The company also says it turns away puppies from USDA-inspected commercial breeders who have received a direct violation, which typically means a problem that affects a dog’s health. When a direct violation occurs, Hunte doesn’t strike the breeder from its books; the company instead offers supplies and educational materials to help get those breeders back up to snuff, so business can resume.

The company is smart about making money at both ends, for sure, which is either an admirable business strategy or a bottom-feeding one, depending on the point of view.

Adapted from The Dog Merchants: Inside the Big Business of Breeders, Pet Stores, and Rescuers, to be published May 2 by Pegasus Books. Order the book through Amazon and other retailers.