Just before midnight somewhere in the western United States, a white pickup truck’s high beams light up a stretch of dark highway.

The driver slows as his three passengers peer through the cab’s front and rear windshields, looking for the headlights of any cars that might catch them in the act of trespassing.

“Let’s be prepared to jump.”

“You have your bag and walkies?”

“Stop here. Here, here, here.”

As the truck speeds off, the three figures scramble quietly off the highway shoulder and into a terrain of scrub brush and jagged gullies. For the next 15 minutes, they walk down an unlit dirt road in near total darkness; even the waning moon’s sliver of light is hidden behind clouds. But their noses tell them they’re in the right place. They’re engulfed in a smell that intensifies as they walk: a blend of barnyard animal, excrement, and decaying flesh. The silence is interrupted only by the crunch of their feet on the sand and then, after a few minutes, sporadic, far-off guttural animal bellowing. They’re approaching their destination, a massive industrial pig farm.

As the three near the facility’s long, low-slung barns arrayed behind giant, man-made lagoons of pig feces and blood, they spot the guardhouse. A TV seems to flicker inside, as it had on the three previous nights. To avoid the building, they leave the road, circling away from the shed through a dry riverbed, and approach the barns from the opposite side.

In the darkness, one of the three intruders switches on a pair of night vision goggles and scans for guards—it’s her turn to remain outside and serve as lookout. The other two pull on Tyvek suits and polyurethane boot covers and run toward the barns.

The team’s leader and smallest member worms through a hole in the enclosure and lifts a bolt on a door to let the other one in. Then the two activists, members of an animal liberation organization known as Direct Action Everywhere, or DxE, start their work: They pull out cameras and begin documenting the inside of the facility, a typical factory farm of the kind that produces the vast majority of the pork Americans eat.

On one side of the two intruders, stretching beyond the edges of their headlamps’ light, full-grown pigs are crammed eight to a cage; the enclosures are just large enough that the activists can see small patches of concrete floor between the animals. On the other side, sows—each at least as intelligent and emotionally sensitive as a dog—are locked individually into metal pens roughly the dimensions of their bodies. The animals in these so-called gestation crates appear not to be able to turn around or even take a step.