Tonight, Captain Picard came back again to his mother's old admonition: "Be careful what you wish for, Jean-Luc. You may get it."

Sitting in his ready room, he again played the record of the Enterprise's brief first passage through the Dyson Sphere. He had played it so many times now that his mind was numbed by it, numbed by what a later computer analysis of that scan had revealed. He had believed the Sphere's interior to be completely lifeless, but a detailed examination of the data by newer and more advanced computers had shown a variety -- a nearly infinite variety, Picard supposed -- of plants and vegetation.

But what they had at first concluded remained true: The Dyson Sphere had seemingly been abandoned by whatever life forms had constructed it. The later analysis had revealed no signs of higher life forms, of intelligent life.

Picard thought he knew every river, every stream, every wrinkle in the world's topography, but he understood that the Sphere's size was every bit as deceiving as it was overpowering, and that for all he thought he knew, there was infinitely more he did not know. The only objects the ship's recorders and the later computer analysis might possibly have missed were a couple of twenty-mile-long elephants. What appeared to be a braided stream was really a river wider than the Earth and descending more than two hundred million kilometers from its headwaters; gazing across whole light minutes of land and sea could draw even the most seasoned explorers into moments of madness.

Picard closed the record of the earlier passage through the Dyson Sphere and opened his captain's log to review the most recent entry.

CAPTAIN'S LOG, STARSHIP ENTERPRISE

Stardate: 47321.6

More than a year has passed since we found Montgomery Scott's ship, the Jenolen, crashed on the outer hull of the Dyson Sphere. More than a year, during which bureaucratic procedure delayed my plans for a return to the Sphere.

We cannot go in until I have assembled my team of Federation-qualified archaeologists. I want scholars who are also efficient excavators -- which means calling on the assistance of Hortas. They can move through rock as effortlessly as a man walks through air. Unfortunately, they are as stubborn as they are efficient -- which has meant more bureaucratic delays.

Two science vessels met us at the end of our first encounter, met us near the Great Wall as we were departing; but the Federation had restricted their exploration of the Sphere entirely to surface mapping and long-range subspace scans. They were under orders not even to try entering Dyson.

Our previous method of entering and exiting the artifact had actually required the destruction of a vessel. The Jenolen held the door to Dyson open while we, in the Enterprise, just barely escaped, having no choice but to fire upon and destroy the vessel blocking our path. We found no obvious way of triggering the exit lock from the inside, and once triggered from outside, a vessel would be hauled in by automatic tractor beams, and the door would close.

Picard closed the log and rubbed at his forehead. He needed a break, a respite from Dyson's vastness, even if it was only a few minutes' escape to a cup of hot tea. Picard heard his mother's voice in his mind once more: Be careful what you wish for, Jean-Luc. You may get it.

He smiled to himself as he realized he was a latterday Spyridon Marinatos. The legendary archaeologist would have appreciated Yvette Picard's warning, when during the summer of 1967 he tunneled into the lost city of Thera, making the discovery of his dreams, and realizing in that same instant that more than his entire lifetime would be required to excavate it. The city was buried under sixty meters of volcanic tephra, and it spread more than two kilometers wide.

Yet for all its overwhelming size, and for all of Spyridon Marinatos's dismay, Thera could easily have been flung into a corner and never found again, had it been situated near one of the "little" doorways that led into Dyson.

The Sphere was dead, of course. Every analyst had agreed on that much: Dyson was a ghost town built to psychopathic proportion, which gave the captain his long-wished-for kinship with Marinatos. He was, at last, being assigned his own archaeological expedition; but as he remembered how Marinatos had fretted over needing more than his own lifetime to discover and catalogue the artifacts of an extinct civilization, Picard wondered what his Greek predecessor would have thought of a ruin whose exploration might require more than ten billion lifetimes.

Be careful what you wish for--

Now, the Enterprise was approaching "the Great Wall of Dyson," about one hundred light years distant from the Sphere. It was a wall of stars -- an actual wall, beyond which no stars at all could be found. No planets. No comets. No meteoroids. Nothing except...

Picard shivered, recalling his now prevailing, probably correct theory about what had happened to the hundreds, perhaps thousands of star systems that must once have existed on the other side of the wall.

Will there come a time when we know such power? Such arrogance? Picard wondered.

"We shall pass through the wall in fifteen minutes," Data announced over the deskscreen.

"I'll meet you on the bridge in five," the captain said and tensed for a moment, then shut the deskscreen off. He was suddenly and acutely aware that his fellow officer was, like the Dyson Sphere, but the handiwork of a clever species, of a momentarily very successful species, that might or might not become as extinct as the Dyson engineers one day.

Dyson was already an artifact. Data might yet become one.

Clever species, Picard thought, then thought again of all those missing stars between the wall and Dyson, and thought again of power and arrogance.

"What are we going to do with the universe?" he said to the empty room, and winced. "Wherefore, what shall we do?"

The universe was full of belittling timeframes. For the Horta named Dalen, the last third of her life, all of those years, had passed so quickly that they seemed only a Vulcan lifespan.

How many more years lay ahead? the Horta wondered.

Maybe fifty thousand?

Yes. Fifty thousand, perhaps, but no more.

This was a mere chip of time, scaled against the age of her homeworld, Janus VI, whose oldest rocks had solidified more than seven billion years ago.

"Only the rocks live forever," said the humans. She could scarcely dream what time must mean to them -- to Picard, and to his predecessor, Captain James Kirk, whom her people would always remember as one of those who had brought them out of the darkness.

When Dalen's ancestors already had many millennia of history behind them, there had existed only a few thousand people on Earth, and they had scarcely begun to wrap their minds around the concepts of building huts and milking goats. Yet during the lifetimes of the oldest of the Horta, billions of them had come and gone. Whole empires had come and gone. And the humans, understanding, now, how to milk power from antiprotons and subspace, had come to the stars and showed no intention of ever going away.

And they had carried with them, in their first deep-range exploratory vessel, the Vulcan named Spock, who was said now to be approaching the end of his own unimaginably short lifetime.

Captain Dalen, for her part, barely perceived the paradox. For her, there was only satisfaction in the realization that some part of the Vulcan who had saved her entire species -- had managed to live a little while longer, if only in crude snippets of DNA.

A little while longer...

It was more than a thousand light years, the Horta knew, from her starship, the Darwin, to the Beta Niobe nova. Curiously, that distant sun could still be viewed starboard and aft, as a dim star circled by a thriving Class M planet.

To the Horta-turned-Federation archaeologist and starship commander, this was the best and worst of times. She oscillated wildly between regret at leaving her quiet life in the caverns of Janus VI, and celebration of escape from her quiet life in the caverns of Janus VI. She was getting used to discovering strange paradoxes in every direction, ever since the humans had opened up the universe to her people. A part of her hated them for this. And a part of her loved them for the same reason.

The surface of Captain Dalen's Homeworld had been nothing except the cold vacuum of empty space, and any who had tunneled straight up and broken through were gushed out, naked, onto an airless deathscape. For their efforts, they left behind only two things: a screaming, outgassing tunnel that had to be quickly sealed, and a very poor inducement for continued space exploration. The theologians and the philosophers around her had declared that there was nothing on the other side of the sky. All life, all matter, and time itself ended at a world-encircling ceiling. And beyond that: nothing. Absolutely nothing.

And then out of nothing, out of that deep, impersonal nothing, had come the miners and the explorers and the starships, bringing with them the tools of subspace communication -- which revealed to the Horta a sky that was full of voices. There had been a time when a nest of newly hatched Hortas had seemed crowded to her, even intimidating. But nothing, it seemed, was so crowded as cold, "empty" space.

One of the most prominent of the latest generation of explorers was, unsurprisingly, also the newest captain of the Enterprise. This Picard fellow wanted to conduct an archaeological survey of the Dyson Sphere now, and he wanted the Darwin's Horta crew on site now. And he had an uncanny way... of getting his way. Captain Dalen's shipping orders had come direct from Starfleet and the Federation Council in San Francisco.

She had no great desire to actually meet Picard. Clearly the man either didn't know or didn't care that Hortas always attended to the task immediately at hand before moving on to the next task, however long it might take. Hortas had the time.

Yet nonetheless she now found herself, her ship, and her crew speeding through subspace toward Picard and the Dyson Sphere. And she had the feeling that whether it took her seconds or centuries to reach her destination two facts remained constant. One: Many of the Federation's assumptions about the nature and origin of intelligent life were, to her mind, probably wrong. Two: Many of the Federation's assumptions about the nature and origin of subspace were probably wrong.

It was nice to know that the universe still had secrets to tell, and that the humanoids, for all their great ships, for all their explored frontiers, were still eager to learn.

Compulsively curious species, the Horta thought, and winced. What, ultimately, were the humanoids going to do with the universe? What would the universe do with them?

"Captain," Data said, "the Darwin's captain informs me that she and her ship will be coming through the Great Wall in three hours."

"It's about time," Picard said, and lowered a hand to his stomach. This time, his passage through the wall had produced a queasy feeling. At present, no dust particles glowed and scratched warp trails on the bridgescreen. Ahead of the prow, the nearest stars were two hundred light years away. This meant that in the view-forward, at normal magnification, there was absolutely nothing to be seen.

The captain had looked out across, and voyaged across, thousands of light years without this same queasiness. He reminded himself that he had known the stars too long to be disturbed by dark, empty places; but little banana fingers were curling around his spine anyway.

This time, he knew that the emptiness had been engineered.

Last time, there had been nothing ahead except Montgomery Scott's distress beacon.

This time, he knew that the most impressive alien artifact ever discovered lay ahead; and while Dyson was huge by any standard, he knew that more than two hundred trillion kilometers of total darkness lay between the Enterprise and the Sphere, and that this, too, belonged to the artifact.

The Sphere was the only object of its kind in all the known regions of the galaxy, although Picard doubted that it was unique. It was simply too attractive a design possibility to have inspired the engineering prowess of only one intelligent species.

Data had named the object after the twentieth-century scientist Freeman Dyson, who had anticipated that some civilization, somewhere, understanding that most of the power from its sun was being poured, wastefully, into the unfillable sink of space, might contrive to enclose the sun.

When he first considered the idea, Picard had suspected that such a vast construction would have to be a Dyson Cloud -- millions of closely spaced habitats clustered around the star, and therefore much easier to construct; but the reality had proved to be a continuous sphere of what seemed to be solid material, imprisoning its sun with no visible breaks in the outer surface -- a delightful feat of engineering, using an advanced materials technology.

The artifact, itself two hundred and four million kilometers in diameter, was located at the center of a cave two hundred light years across. The cave was a perfect sphere carved out of the galactic cloud of stars, gas, and debris. There was no doubt in the captain's mind that the combined mass of thousands of solar systems had been gathered to open this hole in the galactic sea. Ahead, at the center of a stellar desert, was a vast oasis, watered by the energies of a once free star. Why then, as nearly as anyone had been able to ascertain, had the builders abandoned their creation?

With the wall of stars receding aft, the Enterprise began to cross the final hundred light years of desert toward the still invisible Sphere, and Picard could only wonder whether the presumed instability of the central sun was enough to explain why the builders had abandoned their home; he found it strange that they could not have stabilized the star before building so much around it. Was it possible that they had made the Sphere long before they suspected that their sun might develop problems? He found it difficult to accept that such a labor and resource-intensive project could have been undertaken by beings lacking in foresight, even though he knew very well that the psychology of intelligent beings was everywhere flawed. Curiouser and curiouser... it fueled his appetite for the mysterious; and between the desert and the central sun of Dyson, mystery was his only certainty.

He glanced at Deanna Troi, who was seated at her station to his left. She met his gaze in silence for a moment, then said, "I can understand your frustration, Captain. How can we believe that after so much work they simply gave up?"

"Or can we believe that they simply died before they could leave?" Picard answered. "Is it possible that they are still somehow here?"

He stood up and looked around the bridge. His chief medical officer, Beverly Crusher, had ventured up from sick bay only a few moments ago. She stood near Geordi La Forge, who had cleared the neutrino telescope display from his screen and was scrolling through a vast collection of high-resolution scans made during the Enterprise's first, hurried visit into the Sphere. Viewed from a distance of more than forty million kilometers, there was a small white island on the inner surface, that later analysis by the more advanced Federation computer had clearly shown to be covered with Dalmatian-like patches of dark coloration. The patches probably represented forests and near-surface water tables interrupting what would otherwise have been smooth desert terrain. On Earth, Antarctica was considered large enough to be a continent. The desert "island" on Geordi's screen was six times as large, yet here it barely qualified as a beach.

Offshore lay a scatter of microscopic sandbars, ranging down in size from the British Isles to Manhattan Island. There were too many of these "true islands" to be easily counted, much less named. Some were heavily forested, and ground-piercing radar sensors had revealed narrow lines and rectangular depressions that might have been roads and building foundations, unrepaired for millennia. Other islands, at the very limit of resolution, displayed structures that still appeared to be standing intact, as if inhabited only centuries ago, or decades ago. And all of these lands were lost in the center of a strange sea, almost perfectly circular, and as wide as the orbit of Mercury. Geordi had named the sea Great Scott, in homage to his fellow officer and Starfleet engineer Montgomery Scott, the man whose crash beacon had first led the Enterprise to the Sphere.

Geordi turned toward Picard. "I'm with you, Captain," the chief engineer said, "I can't believe that they just left all of this behind. They built a sea wider than four thousand Earths. What happened to them? I can't help thinking it must have been a terrible accident of some kind."

"Hard radiation could have left the Sphere intact," Data said, "while destroying all life. Maybe their sun flared suddenly, driving the creators out and producing a barren landscape resembling Earth after the death of the dinosaurs."

"But some of the islands appear to be covered with highly evolved forests," La Forge objected. "To judge from the heights given by radar imagery, we're talking about trees -- big trees -- possibly even with animals in them."

"The forests could have come through a disaster by the dormancy of their seeds," Data pointed out. "Or they might even have evolved afterward from mere grasses, or from lichens, and a few other stragglers that managed to hold on. The situation here may be similar to what a dinosaur would see, if it could be brought back to Earth today."

Geordi let out a laugh. "You mean, 'Look what happens: I go away for a few million years and the rats take over -- and they've evolved!' "

"Exactly," Data said. "So I would not throw the catastrophe theory overboard quite yet."

"Perhaps the Dyson inhabitants were not driven out by anything," Troi suggested. "Maybe they found something more important to do." More important, Picard thought, would have to be vastly more important to qualify as a reason to leave.

"Or something less appalling to do," said Beverly Crusher. "I find this place extremely fascinating but still disturbing. To build something on such a scale -- eating up whole sun systems in the process. What could have moved them to do it?"

"That," Picard replied, "is one of the things I hope to learn." Disturbing did not seem an apt characterization of the artifact; neither did bizarre. The words just weren't big enough. The right words, he decided, simply did not exist.

"Captain," Geordi said from his station, "I don't think there's been enough time for trees to evolve from grasses. That would have required millions of years, but if you look at the cave of stars--"

Geordi brought the view-aft onto the right side of the bridgescreen. "You'll notice that--" the engineer began.

"--it still has a clearly defined edge in all directions,'' Data finished for him.

Data marveled at the sharp edge revealed by the viewscreen. It was moments like as this that made the android long to be fully human. While the humans envied his positronic memory that contained the accumulated knowledge of multiple civilizations, he was not as skilled as they were at connecting disparate and seemingly unrelated facts. And he sensed something that might be called envy for them, envy for their gift of intuition, as he waxed encyclopedic: "Aft and ventral, Alpha Powell A and Beta Noyes C are moving toward the Great Wall at 5.3 kilometers per second. The normal motion of stars in the galaxy should have blurred the wall's edge relatively quickly, in the same way that constellations will change in the sky of any world in a matter of a few tens of thousands of years."

"I see," Picard cut in, "that such blurring is not even visible here--"

"Yes, Captain," Data continued. "This cave hewn out of the starfield cannot be much more than a hundred thousand years old, so by association the Sphere is the same age. As stars measure time, the Dyson Sphere was built only yesterday."

"Built by whom?" Picard asked. "That's what troubles me. Is there a race we know that could trace its ancestry to a people who would scoop out a volume of space two hundred light years across to complete an engineering project?"

"Captain..." Troi began, her voice laced with hesitation and concern.

"Yes, Counselor. Think of people with a voracious appetite for power. We must consider the possibility that this is the archaeology of the Borg."

"A fascinating hypothesis, Captain," Data said from his station.

"And like most hot speculations, it's probably wrong," Picard replied. "But criminal behavior does spring to mind, despite the impressive display. An inside-out world with more habitable area than a quarter billion Earths -- it makes me think of all the solar systems that will not be here to develop intelligent life."

Troi said, "Perhaps it was guilt over that very realization that led to the Sphere's abandonment. That guilt may have worked on them for a long time."

"I wouldn't count on that," Picard said. "I wish I could believe that they became, like the Ionian Greeks, a race of philosophers and dreamers, and turned their back on instrumentalities." He shook his head. "Maybe the ultimate consumers went at last to another extreme, and threw off all material possessions. Maybe, instead of the Borg, the road to Dyson leads to--"

"No, not the archaeology of the Q," Troi said.

"A cosmic joke, either way."

"Captain," Data said, "we have few facts from which to reason."

"Quite right, Data. But the possibilities are finite. We can guess the answer -- but it will only be helpful if we can later prove it true."

"Humans find it helpful to work in that way," Data said, "backward from a guess. Your great physicist, Richard Feynman, advocated such a procedure."

"But you find it... confusing?"

"A leap into the dark, perhaps," Data replied.