At the eastern end of Orange County, many of the canyons are still home to more coyotes, bobcats, mountain lions, and deer than people. Carved into the foothills of the Santa Ana Mountains, some are mere ravines, others less narrow, all thick with trees and brush, a refuge for the contemplative, for those who dislike urban and suburban life, and for various eccentrics.

The serpentine, undulatory tossed-ribbon of a road unraveled as if it were the last feeble construction of the declining civilization that had built it. Huge California live oaks overhung the pavement, trunks and limbs char-black in our headlights.

The houses were well separated even at the civilized end of the road. They grew farther apart the deeper we penetrated the canyon, the name of which I will not provide, for reasons soon obvious.

With isolation came a different mood. Geological details seemed more dramatic, slopes steeper and rock formations more suggestive of violence. The woods thrust at us and the brush bristled aggressively, as though we had passed through a membrane, leaving benign Nature, entering a preternatural place in which a malevolent consciousness lived in the darkness, was the darkness, watched, and waited.

When I saw lamplit windows back among the trees, they no longer appeared warm and welcoming, but eerie and forbidding, as though the unseen structures were not houses but abattoirs, temples of torture, and fiery forges in which were cast images of strange gods.

The two-lane blacktop continued, but we turned onto a narrower gravel road that looped a few miles before rejoining the paved route. This one-lane track, which climbed the lower slopes of the canyon wall, was used largely by agents of the state forestry department.

Wet weeds swished against the sides of the Mountaineer, and some semitropical plant, with pale leaves as large as hands, slid its many palms across the passenger-side windows.

After some distance—for reasons soon obvious, I will not say how far—we came to a lay-by, where I could park alongside the track. When I switched off the engine and headlights, the darkness was as absolute as if we were in a windowless building. Only the drumming of the rain proved we remained outdoors.

The Boom house faced the paved road that we had departed. But we were not entering by the front door.

“We’ll be eaten alive, going in this way,” Milo predicted.

“No mountain lion will attack a group of people,” Penny assured him. “They stalk what’s smaller than they are—and what’s alone.”

“Lassie and me are smaller,” Milo said, and the dog whined.

“But neither of you is alone,” I said.

Milo was not a fan of wilderness. He embraced civilization and all its charms, regardless of its humongous carbon footprint.

Hoods up, with two flashlights, we got out into the rain, and I locked the Mountaineer.

Moving away from the gravel track, we waded through weeds and between trees until we came to a small low rock formation from which, in daylight, you could look down a gentle slope, through woods to the canyon floor, although not quite as far as the paved road.

Scattered nearby on the loamy floor of the forest, among ferns, were several stones, each a unique shape, but each weighing precisely 4.4 pounds. Any one of them was a functioning key.

I carried a stone to the rock formation and placed it precisely where Penny indicated with her flashlight.

We stepped back, off the lock slab, which would not move if either too little or too much weight was applied. After a moment, a five-by-six-foot horizontal portion of the formation pivoted along what seemed to be natural fissure lines, cast aside the 4.4-pound lock key, and stood on end: a trapdoor.

Although it appeared natural, the rock formation was man-made. Thirty-eight years previously, Grimbald, his intriguing father, his unique mother, his unusual brother Lenny, his irregular brother Lanny, his curious brother Lonny, his remarkable sister Lola, and his wondrous strange Uncle Bashir had joined with Clotilda and seven members of her uncommon and baffling family—all sixteen of them committed survivalists—to construct a combination home and end-of-the-world retreat prior to Grimbald and Clotilda’s marriage, as a wedding gift.

You can think of this project as like an Amish barn-raising for newlyweds, except that none of these people was Amish, no barn was involved, they used power tools, they cussed sometimes, most of the construction was done in secret without building-department permits—and, if what we believe we know about the Amish is true, Grimbald and Clotilda began their married life with a great many more guns than did the couple for whom the barn was raised.

Although both Grimbald’s and Clotilda’s families are no more forthcoming than the great stone heads on Easter Island, although they have a high regard for subterfuge and hugger-mugger, they have hinted that they have come together to build similar retreats for one another in Northern California, Oregon, Nevada, and Montana.

Under the pivoting-rock trapdoor, our flashlights revealed a long narrow flight of concrete stairs and a stainless-steel handrail. Penny led, Milo followed with Lassie, and I brought up the rear, descending as if into a storm cellar.

Halfway down the stairs, we came to a one-foot-wide, eighteen-inch-high recess in the left-hand wall. A steel rod with a rubber handgrip protruded from a slot in this recess. It was in the down position.

As Penny pushed the rod up, it made a ratcheting noise. I heard gears clicking somewhere.

Overhead, the rock trapdoor pivoted shut with a gasket-muffled thump. Without the inflowing air, the stairwell smelled of lime and wet dog.

After the end of the world, reliable electrical service will most likely not be available from the power company—nor, I might venture, will you be able to buy those delicious little chocolate-covered doughnuts that are currently to be found in any supermarket. Consequently, the three secret entrances to Boom World are opened and closed by a system of weights and counterweights riding on cables, controlled by hand-operated levers and wheels, a system so mechanically complex that I would rather die horribly in Armageddon than try to learn how to operate and maintain it.

At the bottom of the stairs was your standard impenetrable steel door. It looked not much different from the one protecting access to the panic room in Marty and Celine’s peninsula house. The door had no keyhole; the lock-release levers were concealed in the floor drain.

The grid bars in the drain grate formed approximately half-inch square holes, except in each of the four corners, which featured a trio of larger openings. If you knew into which two corners to insert your fingers, you could lift the grate out of the way, exposing the drain and the hidden lock-release levers.

In the event that you inserted your fingers into the wrong holes, the grate would not release but would amputate your digits.

By the time my courtship of Penny matured to the inevitability of marriage, I had gotten to know her family, and I had on one occasion half-seriously wondered if, to protect their daughter from sexual predators, they had designed for her a wardrobe of cleverly booby-trapped clothing that would sever my hands at the wrists if I put them anywhere they had not been invited.

Taking every measure that might thwart Shearman Waxx, we had not called ahead to let Grimbald and Clotilda know we were coming. Therefore, even if we lifted the drain grate properly and correctly used the hidden levers to unlock the blast-resistant door, we would be at great risk crossing the threshold. The Booms were in lockdown mode, which meant additional lethal devices had been engaged in the hallway beyond this antechamber.

Beside the door, a capped pipe protruded from the wall. In the center of the two-inch-diameter cap was a pull-ring that connected to a taut, small-link chain inside the pipe. The pipe—and the chain—led into the main room of the shelter. When the near end of the chain was pulled, the far end swung a miniature brass hammer against a brass bell, producing a single loud, clear note.

With a series of pulls on the chain, Penny rang out her personal passcode. She waited ten seconds and rang the code again.

I could hear the notes echoing faintly through the pipe from a distant room of Boom World.

Half a minute later, mechanically triggered clockwork gears began to turn inside the steel barrier, retracting a series of bolts from the jamb. The door opened.

Penny confidently led the way across the threshold into the Hall of a Thousand Deaths.