The satellites were able to push through the center of each hole in the negative mass lattice where the inverted gravity was at its weakest. Anna moved one down to the next level, dipping it into the shoal of tiny pale scintillations that swirled across the gulf between the second and third lattice spheres. Its sensors had trouble tracking the dense will-o’-the-wisps, but eventually the physicists determined it was a tenuous cold plasma, aggravated by the emissions of the exotic matter below, and confined to the gulf by the negative mass above.

Analyzing the exotic matter proved even more difficult than with the previous two lattice spheres. They had to launch a whole squadron of large Armstrong-class satellites with their powerful and comprehensive sensor suites. It took a further two weeks before they’d charted the energy currents seething like photonic tempests in the plasma between the two exotic matter spheres. After that, they were able to pilot a satellite through the fourth lattice sphere.

When the first Armstrong satellite passed through it found no further spheres. Instead, the space in the middle, measuring sixteen thousand kilometers in diameter, housed a series of concentric rings, all of them aligned with the plane of the barrier outside. The outermost, thirteen thousand kilometers across, the crew immediately named the daisy chain. It was a sequence of lenticular disks linked together by a black cable. Next in was a simple ring of green matter, so smooth and uniform it was impossible to tell if it was rotating. Then a braided ring whose thick silver strands moved sinuously around each other like oiled serpents. One of pure scarlet light. More solid loops. Globes, hundreds of thousands of them, strung together in a dense necklace that the bridge officers likened to a strand of alien DNA, twisting around each other as they rotated around the center. Sparks: a wide band of emerald and amber lightpoints trailing cometry tails as they orbited in both directions, though never colliding. There was one of water, or some clear liquid, with a surface beset by waves. Right in the center was emptiness, a little patch of darkness into which light fell.

It was God’s own orrery.

Talk in the starship’s canteen was that the lattice spheres powered the rings, or vice versa. Either way, they were all convinced now that the Dark Fortress was the barrier generator.

One by one, the satellites were ordered down toward the rings. One by one they lost contact with the Second Chance. The center of the Dark Fortress was an energistic maelstrom. Human technology could not survive within it. Watching the displays that showed tides of quantum distortions raging chaotically around the wounded satellites, some of the physics team claimed the rings didn’t—couldn’t—even exist in normal spacetime.

What everybody on board wanted to know was if there was a corresponding opening on the other side of the Dark Fortress.

“There’s no way we can get anything across the center and past the rings,” Tunde said. “If we’re going to try this, we’ll have to program a satellite to fly around in the gulf between the outer shell and the first lattice sphere. It’ll have to operate in autonomous mode, we don’t have enough satellites to act as a relay chain over that distance.”

“It’s a waste of time,” Oscar said. “I don’t believe there’s a hole there. There’d be no damn point to the whole barrier if there was.”

“I don’t think there is either,” Wilson said. “But you know we have to look. Anna, program a Galileo for the assignment.”

The flight took three days. When the Galileo reemerged into communications range, its sensor logs showed the shell opposite the hole was continuous. It had searched over twenty thousand square kilometers. Wilson ordered it to be refueled, and sent it out again. After seven flights, it had scanned the entire hemisphere on the other side of the barrier. There was no hole, no passage through to the imprisoned star.

Three months after they discovered the Dark Fortress, Wilson called Oscar and Tunde to his cabin for a mission conference. “I need to know if we’re going to learn anything more from the Dark Fortress,” he said to Tunde.

“Are you joking?” the surprised physicist asked. “There is more exotic physics in there than the human race has discovered since an apple fell on Newton’s head.”

“I’m sure there is. But now we have the major components identified, how much can you and your team realistically add to that? I mean, we don’t even know if this really does generate the barrier.”

“It’s a logical conclusion.”

“Admittedly, yes. But can you prove it? More importantly, can you prove it with the sensors and instruments we have available on board?”

Tunde looked defiant for a moment, but eventually nodded reluctantly. “No. Not a chance, really. As you say, we can map what’s there. But determining function and interconnectivity… On this scale, it’s the kind of project which would absorb every living theorist for the next two centuries. We need a bigger ship; in fact, we need to establish an outpost the size of the High Angel, and with its manufacturing capacity. The Commonwealth will have to open a chain of wormholes out here, that’s the only way we can apply the kind of resources we need to crack this.”

“It’s not going to happen,” Oscar said. “Oh, I agree, it should. But from a political point of view, all you’ve got here is the mother of all esoteric physics problems. That doesn’t gain you the kind of funding you’re talking about.”

“Nigel Sheldon will understand,” Tunde said.

“Yes, he will,” Wilson said. “More than anybody, he made this flight possible. But even he can’t carry the entire Commonwealth Senate, not for that kind of financial commitment. If we’d found anything out here, anything that indicated why the barrier was established, any hint of a current threat to the Commonwealth, then we might earn ourselves a couple of return missions at the very least. But it’s an enigma. And we’ve lived with enigmas for a long time now. We’re shocked and excited by them at first, then we just learn to live with them. Eventually, we don’t even question them anymore. Look at the Silfen. Why don’t electronics work on their worlds? How the hell do they really travel between star systems? Our popular myth has it there are forest paths between worlds. That’s what the more whimsical members of our race believe. More practical people believe they spread themselves across the galaxy with arkships millennia ago. It doesn’t matter, because we live with it, it doesn’t affect us. Now as far as we can determine, the barrier, for all its grandeur, isn’t going to affect us either. There are no alien battle fleets waiting out here to blow Earth to pieces and steal our gold and our women. This is just one more incomprehensible relic that will take us five hundred years to understand. One day, after that, you and I will be standing here and laughing at how puzzled we once were.”

“You’re taking us home, aren’t you?” Tunde realized.

“Not immediately. But we’ve certainly devoted enough time to the Dark Fortress. Unless either of you have a viable alternative, I’m going to continue with our flight around the barrier. After that, if there’s nothing else to be found, we’ll examine the poles as originally planned. We might follow up with a fast examination of Dyson Beta. I’d like to confirm that it is the same before we head for home.”

“I’ll concur with that,” Oscar said. “Team leaders are getting asked how much longer the investigation is going to last. Nobody has actually complained yet, but I’d say it’s time to move on.”

They both looked at Tunde.

“All right,” he said. “We do have enough data to keep the universities busy for a decade. But I hope to God you’re wrong about the next stage of the project. Understanding the technology in the Dark Fortress would elevate our species to unbelievable heights. We could become transgalactic, for heaven’s sake; there really would be no limits to what we could achieve.”