It was a memory of something Alan Stern had said to him one night—Stern the physicist, who might have perished in the trouble last night; Stern, his uncle.

Howard had been sixteen years old, a math prodigy with a keen interest in high-energy physics, about to be launched into an academic fast track that both excited and frightened him. Stern had come to visit for a week that summer. He was a celebrity: Alan Stern had appeared in Time magazine, “preeminent among a new generation of American scientists,” photographed against a line of radio telescopes somewhere out west. He had been interviewed on public television and had published journal articles so dense with mathematics that they looked like untranslated Greek papyruses. At sixteen, Howard had worshiped his uncle without reservation.

Stern had come to the house in Queens, bald and extravagantly bearded, infinitely patient with family gossip, courteous at the dinner table and modest about his career. Howard had learned to cultivate his own patience. Sooner or later, he knew, he would be left alone with his uncle; and the conversation would begin as it always began, Stern smiling his strange conspirator’s smile and asking, “So what have you learned about the world?”

They sat on the back porch watching fireflies, a Saturday night in August, and Stern dazed him with starry sweeps of science: the ideas of Hawking, Guth, Linde, himself. Howard liked the way such talk made him feel both small and large—dwarfed by the night sky and at the same time a part of it.

Then, when the talk had begun to lull, his uncle turned to him and said, “Do you ever wonder, Howard, about the questions we can’t ask?”

“Can’t answer, you mean?”

“No. Can’t ask.”

“I don’t understand.”

Stern leaned back in his deck chair and folded his hands over his gaunt, ascetic frame. His glasses were opaque in the porch light. The crickets seemed suddenly loud.

“Think about a dog,” he said. “Think about your dog—what’s his name?”

“Albert.”

“Yes. Think about Albert. He’s a healthy dog, is he not?”

“Yes.”

“Intelligent?”

“Sure.”

“He functions in every way normally, then, within the parameters of dogness. He’s an exemplar of his species. And he has the ability to learn, yes? He can do tricks? Learn from his experience? And he’s aware of his surroundings; he can distinguish between you and your mother, for instance? He’s not unconscious or impaired?”

“Right.”

“But despite all that, there’s a limit on his understanding. Obviously so. If we talk about gravitons or Fourier transforms, he can’t follow the conversation. We’re speaking a language he doesn’t know and cannot know. The concepts can’t be translated; his mental universe simply won’t contain them.”

“Granted,” Howard said. “Am I missing the point?”

“We’re sitting here,” Stern said, “asking spectacular questions, you and I. About the universe and how it began. About everything that exists. And if we can ask a question, probably, sooner or later, we can answer it. So we assume there’s no limit to knowledge. But maybe your dog makes the same mistake! He doesn’t know what lies beyond the neighborhood, but if he found himself in a strange place he would approach it with the tools of comprehension available to him, and soon he would understand it—dog-fashion, by sight and smell and so on. There are no limits to his comprehension, Howard, except the limits he does not and cannot ever experience. So how different are we? We’re mammals within the same broad compass of evolution, after all. Our forebrains are bigger, but the difference amounts to a few ounces. We can ask many, many more questions than your dog. And we can answer them. But if there are real limits on our comprehension, they would be as invisible to us as they are to Albert. So: Is there anything in the universe we simply cannot know? Is there a question we can’t ask? And would we ever encounter some hint of it, some intimation of the mystery? Or is it permanently beyond our grasp?”

His uncle stood and stretched, peered over the porch railing at the dark street and yawned. “It’s a question for philosophers, not physicists. But I confess, it interests me.”

It interested Howard, too. It haunted him all that night. He lay in bed pondering the limits of human knowledge, while the stars burned in his window and a slow breeze cooled his forehead.

He never forgot the conversation. Neither did his uncle. Stern mentioned it when he invited Howard to join him at the Two Rivers research facility.

“It’s nepotism,” Howard said. “Besides—do I want this job? Everyone talks about you, you know. Alan Stern, disappeared into some government program, what a waste.”

“You want this job,” his uncle told him. “Howard, you remember a conversation we once had?”

And he had recalled it, almost word for word.

Howard gave his uncle a long look. “You mean to say you’re pursuing this question?”

“More. We’ve touched it. The Mystery.” Stern was grinning—a little wildly, Howard thought. “We’ve put our hands on it. That’s all I can say for now. Think about it. Call me if you’re interested.”

Fascinated despite himself—and lacking a better offer—Howard had called.

He had been investigated, approved, entered onto the DOD payroll; he had shown up three days ago and toured a part of the facility… but no one had explained its essential purpose, the fundamental reason for these endless rooms, computers, concrete bunkers and steel doors. Even his uncle had remained aloof, had smiled distantly: it will all be clear in time.

He came over the rise and saw the buildings gilded with blue light; saw the smoke rising from the central bunker. Worse, he saw a fire department ladder truck and chase car inching down the access road, the image fluid and indistinct.

He could not imagine what this veil of light might mean. He knew only that it represented some disaster, some tragedy of a bizarre and peculiar kind. No one was moving in the complex, at least, no one out in the open. The facility had its own fire control team, but it wasn’t anywhere near the smoldering central bunker—at least, as far as Howard could tell. The blue light made his head swim.

Maybe they were all dead. Including his uncle, he thought. Alan Stern had been at the center of this project, that much had been obvious; Stern had been its lord, its shaman, its guiding presence. If the accident was lethal it would have taken Stern first of all. All this fluorescence suggested some kind of radiation, though nothing Howard could pin down—something powerful enough to kick photons out of the air. He knew there was radioactive material at the facility. He had seen the warning labels on the closed bunkers. They had given him a film badge as soon as he passed the gate.

That was why he’d chased the Two Rivers VFD all the way out here. He didn’t think small-town volunteer firemen were trained or equipped to fight radioactive fires. Most likely they weren’t even aware of the danger. They might blunder into an event more deadly than they could guess. So Howard had jumped into his car and rushed after, meaning to warn them—still, meaning to.

But he saw the trucks hesitate and stop, then reverse, wobble, retreat.

He drove down the hillside to meet them.

Assistant Chief Haldane saw the civilian automobile come over the rise, but he was too dazed to worry about it. He had climbed out of his car, vomited once into the young weeds by the side of the road, then sat on a wedge of natural granite with his head in his hands and his stomach still churning.

He didn’t want to see anyone, didn’t want to speak to anyone. What mattered was that he was beyond the border of blue light, that he had found his way back into the world of sanity. His relief was immense. He took deep, cleansing gulps of air. Pretty soon he would be back in his sane house in the sane town of Two Rivers and this nightmare would be over. All these buildings could burn to the ground as far as he was concerned—the better if they did.