0002 hours, September 7,2552 (Military Calendar) \ ONIunderground facility, planet Reach.

Fred followed the trail of odd symbols along the left-hand stone wall until they twisted into a spiral mosaic and vanished into ever-smaller curls. The symbols were part of the rock, composed of glittering mica inclusions in the granite matrix. There were a series of squares, triangles, bars, and dots, similar to Covenant calligraphy he had seen—but at the same time it was simpler, cleaner, and when Fred focused on them, the characters seemed to blur around their edges and fade from his stare.

He blinked, and the symbols were there again.

Following these symbols like a trail of bread crumbs had been his primary mission for the last five days. Dr. Halsey and the Spartans had explored the extensive caverns, hoping to find two things: a way out, and what Dr. Halsey called "the most important discovery of the millennium." She had, however, refused to speculate on what exactly this discovery would be. "I'm a scientist," she'd told them, "not a soothsayer."

Fred would have settled for finding an airhole to the surface— but he recognized that the symbols were important, too. They were important because the Covenant thought they were important. And that made whatever Dr. Halsey was searching for worth finding, if only to keep the enemy from getting it.

The Covenant hadn't stopped digging overhead, although the pace and methods they used had changed. There had been no further explosions. There was only the constant and gentle scraping sound of equipment as they slowly but steadily removed the mountain. Every hour the sound intensified as they drew closer. Fred had set his audio filters to screen out the noise so he could concentrate.

Five days. It hadn't seemed that long. They worked, they rested, they slept, and they waited. Dr. Halsey had taught them word games like twenty questions and simple cipher, at which they all became extremely proficient—so much so that she quickly stopped playing. Dr. Halsey was not a graceful loser.

The time had melted away. Maybe it was the darkness, the lack of any temporal reference like the sun, moon, and stars, but the hours had lost their meaning.

He paused to stretch his Achilles tendon, recently stitched and fused by Dr. Halsey. Aside from some stiffness, it was almost back to normal. He had almost torn the tendon off, running on the injury.

Dr. Halsey had patched them all up; she had even flash cloned Kelly a new partial lung, which she successfully grafted. In her tiny field medical kit, the doctor had a handheld MRI, a sterile field generator, even a shoe-box-sized clone tank for organ duplication.

She had also installed the new MJOLNIR parts in their existing armor. These upgrades were in field-testing and not certified, she had explained, but she gauged their need sufficient to justify the risk of using the new equipment.

Kelly received an improvement to her neural induction circuits, giving her twitch response time a speed boost. Vinh had a new linear accelerator added to her shield system, effectively doubling its strength. Isaac had a new image-enhancing computer installed. Will received a better tracking system on his heads-up display, which improved his accuracy at distances up to a thousand meters.

Fred flexed his bare right hand. Dr. Halsey was installing his upgrade now—new sensors that would boost the sensitivity of his motion tracker. Without the single gauntlet, Fred felt vulnerable. The Master Chief would have told him not to rely on his armor or weapons—rely instead on his head. It would protect him better.

He wondered how Blue Team—John, Linda, and James—had fared. And what of the rest of his own team? Had anyone at the generator complex survived?

He didn't want to think about them—but he couldn't help it. Maybe it was the darkness and the constant weight of the earth around him.

What if they died here? Not died fighting, but just died here. In a way, that wouldn't be so bad. Fred had faced death a dozen times, brushed so close to it he had stared it in the face until it blinked and turned away.

This was different, though. He didn't want to die, not without knowing if the other Spartans were still out there fighting. Not if they still needed him.

He sighed and absentmindedly brushed his fingertips across the odd symbols. They were as smooth as glass, and their edges were sharp. These crystals could be a natural phenomenon. He had seen similar inclusions in the museum on—

Fred felt a hot pain in the tip of his finger. He drew his bare hand away and a tiny track of blood smeared the rock.

The glittering symbols on the wall took on a greasy cast, and the reflection from his helmet lights thickened and almost seemed to be absorbed by the minerals.

He flicked off his helmet lights. The symbols in the rock emitted a faint illumination of their own: a soft reddish glow like heated metal. The light intensified and spread across the spiral on the wall, starting from where his blood had fallen; those symbols warmed to a pleasant orange, then yellow-gold.

A new symbol in the center of the spiral appeared that hadn't been there a second ago . . . or perhaps it had been, but had lain just beneath the surface. It heated and became increasingly visible, a single triangle that glowed white.

Fred was inexorably drawn to this central figure. He reached for it; there was no heat. He slowly stretched and touched the symbol with his exposed fingertip.

Warm white light raced along the spiral of symbols, then traced a path down the hallway and into the distance. The entire cavern seemed sudden alive with radiance and shadow. Even with the step-down luminosity filters in his helmet, Fred had to blink and squint.

The wall before him rumbled and seams appeared at the central figure, dozen of lines that curved in a radial pattern—and then pulled away to reveal a corridor behind.

Fred realized that he was holding his breath. He exhaled.

This new corridor was twenty meters high—large enough for a titan to stride down its length. It vanished into the distance, a straight line that gently sloped deeper into the earth. The floor was paved with asymmetric blue tiles patterned to look like waves lapping upon a shore. Four-meter-tall symbols of gold were centered and inlaid into the mirror-smooth walls. These giant triangles, squares, bars, and circles began to emit the same soft light... and Fred felt his foot shuffle forward.

He stopped, shook his head, and looked away. He checked his radiation counter; it pulsed, and then fell back to a normal background count.

He keyed the COM. "Doctor Halsey, I think I've found what you've been looking for. Sending video feed now. Copy?" There was a long pause. The COM was open, but Dr. Halsey wasn't responding.

"Doctor Halsey, copy?"

"Yes," she finally said over the COM. "Don't move, Fred. And don't touch anything. Excellent work. Kelly, Isaac, Vinh, Will— meet me at Fred's location."

Fred wanted to stare at the gold symbols and the light they cast, but something warned him that this would be dangerous. He had long ago learned to listen to that inner voice when on patrol or in the heat of battle. It had saved him from dozens of ambushes. He kept his eyes on the dirt floor of the tunnel. There was something too fascinating and nearly familiar about those symbols. They reminded him of the Greek mythology that Deja, the Spartans' first teacher, had taught—legends of hauntingly beautiful creatures who lured the unwary to certain death. Sirens.

He checked his rifle. The ammo counter read full, but he hit the magazine release and visually confirmed it. He slapped the clip back into the receiver. This simple operation cleared his head.

He detected four blips on his motion tracker—they glowed green, indicating fhendlies. Kelly, Vinh, Isaac, and Will jogged up next to him, weapons ready. "What is this?" Will whispered. The golden glow reflected in his helmet's faceplate.

"Careful," Fred warned them. "Filter the light. Go to blackand-white image enhancement."

He got four blue acknowledgment signals, and then Fred switched to BWIM display. Funny that he hadn't thought of that for himself. Only when the safety of his team was at stake did he think clearly.

Dr. Halsey ran along the tunnel and halted, panting, next to the Spartans. "Yes," she said, wheezing. "Yes, this must be it—what Ackerson was searching for. And most likely"—she glanced at the roof—"what they are looking for, too, I imagine."

Dr. Halsey ignored the curious symbols and the light, and strode into the new corridor. "Hurry," she told them. "I fear we've set something in motion, and our visitors upstairs might know it, too."

Fred assembled his team to form up around Dr. Halsey. Kelly took point, and the rest of them created a loose box around her.

Dr. Halsey handed Fred his missing gauntlet. He took it and wriggled his fingers into the armor, pulled it snug, and sealed the locking collar around his wrist. Diagnostics ran and confirmed that his armor was whole again. His motion tracker pulsed on his heads-up display.

The hallway changed as they continued down its length. The golden light faded along the ceiling, and inky black covered its expanse; tiny stars winked on and twinkled. Fred added color to his display; he wanted to see this. Moons wheeled overhead; silver-gray orbs, pockmarked with meteorite impacts, spun in wide orbits. Along the walls, tall green bamboo-like grass sprouted and grew up the curved surfaces.

Dr. Halsey brushed her fingertips along the wall, and the grasses wavered at her touch. "Semisolid holography," she said without halting. "No visible emitters. Interesting. We should investigate this later," she said and increased the pace of her stride. "If there's time."

The holographic environment cycled to an arid moonscape: deep craters and sterile light; it became a volcanic world with lava flowing alongside them. The air wavered with heat. In each transformation the golden symbols remained on the walls, leading them through the illusions.

The corridor emptied onto a landing that overlooked the largest room Fred had ever seen. Kelly stepped onto the landing, looked, and waved them forward.

They stood on one of a dozen tiered levels that encircled the room; there was no railing. Fred leaned over the edge. It was at least one hundred meters to the floor below. The room was approximately circular and three kilometers in diameter. The floor was blue and seemed to shift as a billion tiny tiles flexed and rearranged themselves into frustratingly familiar patterns. The ceiling was a dome with a holographic golden sun, blue sky, and cottony clouds that morphed into spheres, puffy pyramids, bars, and cubes. And in the center of the floor was a pedestal flickering with a faint light.

Isaac held up his hand. "Listen," he whispered over the COM.

They all froze, and Fred strained to hear. There was nothing. Fred turned up his aural amplification to maximum gain. He heard the creak of their armored joints and five faint heartbeats but, other than that, silence.

"They've stopped," Fred said, and pointed overhead. "The digging." "I don't like it," Dr. Halsey said. "The Covenant aren't known for giving up on anything they start. We'd better continue."

Kelly removed the clip from her magnum, cleared the chamber, and then slid a self-installing piton down the length of the barrel. She shot it into the stone wall, and the metal shard implanted ten centimeters and blossomed with sharp talons, securing the shaft to the wall.

Vinh handed her a coil of black rope. She clipped one end to the piton, then tossed the rest over the edge. Isaac and Will stood on the lip and swept the vast open region with their weapons. Kelly jumped and rappelled to the bottom. A moment later she gave the all-clear signal.

Will and Isaac followed her to the floor. Fred tied the rope around Dr. Halsey's waist and lowered her gingerly down after them. He and Vinh took up the rear.

The floor of the great room wasn't the same tile as in the corridor above. It was still blue tile, but these were squares and circles and bars and triangles. If the symbols were a language, Fred stood upon a million words; he wished he'd been issued a dictionary.

Dr. Halsey paused to examine the tiles as well. "If only we had the time," she muttered, and then walked toward the light gleaming in the center of the chamber.

The Spartans formed up around the doctor again, but Fred's instincts warned him that this wasn't a good idea. He couldn't get his bearings straight. The room was big, large enough that it felt as if they were outside. It threw him off. He had an odd sense of vertigo, almost as if the floor was tilting and he was now walking on the roof.

Dr. Halsey increased her pace, but the distance to the center of the room didn't seem any closer; in fact, they seemed more distant from the center than when they had started out from the edge of the room.

Fred turned down the gain on his display until everything was a faint black-and-white blur. He focused on his motion tracker and saw that the Spartans and Dr. Halsey were now separated across two dozen meters.

"Everyone stop," he said. "Regroup. We're getting scattered."

They halted and edged back into formation.

"There must be another way," Dr. Halsey said. She reached into her lab coat pocket and removed a ball bearing. "The floor slopes toward the center," she observed. She set the bearing on the floor and gave it a gentle push. The bearing rolled, then curved, and spiraled back to a stop.

"This is getting too weird," Fred muttered. "Kelly, you have the best aim. Close your eyes, pick a direction, and we'll follow."

"... Affirmative," she whispered.

The Spartans set their hands on each other's shoulders and marched, not toward the center of the room but to a spot that Kelly picked, apparently back the way they had come.

Fred turned off his display and watched his motion tracker. They were all together and another blip appeared, one that Kelly was leading them straight to.

Another twenty meters and she halted. "Look." Fred snapped on his heads-up display, and sapphire-blue light filled his vision. They stood before the source of the glow in the

middle of the room. There was a pedestal made of the same gold material as the symbols in the corridor, and floating above it was a fist-sized crystal, tapered to a point at either end. It spun, and the facets along its centerline folded and shifted like the pieces of a puzzle.

Dr. Halsey reached for it and then hesitated. "Radiation?" she asked. Fred checked his counter. "Normal background levels," he reported.

"We must take this with us," she whispered. "Study it. Or destroy it if necessary to keep the Covenant from getting it." She touched the crystal, and its light dimmed. For a moment the light appeared to be absorbed by Dr. Halsey's palm.

Static washed over Fred's display, his shields shimmered, a squeal blasted through his speakers, and his motion tracker momentarily made contact with a thousand targets swarming through the great room. His radiation warning flared red and then faded.

"Radiation spike," he said. "Analysis says lots of neutrinos, but I'm unable to determine the type—it's something not in the computer's database."

"Is it safe now?" Dr. Halsey asked, peering into the crystal she gripped in her tiny hand.

"Seems so," Fred told her, "but Doc—"

"No time for debate," she said. "Neutrino radiation will penetrate the rock between us and the surface."

"They'll be able to get a fix on our position," Kelly said. "All they need is three ships nearby to triangulate. We need to get out ofhere—fast."

"Which way?" Isaac asked Fred. "Back the way we came, or deeper in?" "There was no way out from the titanium mines," Fred replied. "So we go deeper." An explosion rocked the earth and deep thunder rumbled, but rather than diminishing, this thunder got louder, closer.

Fred's shadow lengthened, and its edges sharpened.

He whirled toward the source of the intense white light— directly overhead, a spot in the dome: The holographic scenery of stars and moons bleached and vanished. He spun Dr. Halsey around so she faced away, then covered her head.

The stone ceiling melted and peeled back as if it were thin plastic hit with a blowtorch—an angled shaft of dazzling white radiance appeared and blasted into the tiled floor, five hundred meters from their position.

Then it was gone and the room fell into darkness punctured only by a ray of faint sunlight that streamed in through the hole above. Where the beam of hard light had contacted the floor, a precision-milled hole had been etched fifteen meters deep.

Dr. Halsey said, "What was—"

"Energy projector," Fred told her, blinking away the black dots that filled his vision even though his step-down filters had absorbed the brunt of the light. "Only the big Covenant ships have them. There's got to be one of them—"

The cut shaft filled with a beam of purple light. It sparkled and shimmered with motes of dust.

"Grav lift," Fred shouted. "Incoming! Isaac and Vinh, take our six. Will, you're with me on Doctor Halsey. Kelly, find us a way out."

Kelly ran in a line directly away from the gravity beam. A dozen Elites floated down through the shaft, and fired while still in the air. Plasma bolts slashed at them from the distance.

Fred and Will grabbed Dr. Halsey and moved her behind the pedestal, out of the line of fire. Isaac and Vinh fell back and opened fire.

"Suppression fire!" Fred barked. "Keep them pinned in that crater!"

The Spartans fired several bursts, but more Elites were drifting down, along with a Shade—a portable plasma turret. If they stayed here, they'd be overrun.

"Fall back," Fred told them over the COM. "It's too hot."

Kelly sprinted, digging in her heals with such force that the tiles buckled and shot out behind her. "Passage," she reported. "Ground floor. Dead ahead. I'll enter and clear."

"My apologies, Doctor," Fred said and unceremoniously scooped Dr. Halsey up in his arms. "Everyone move! Vinh, Isaac, drop those det sacks to cover our tracks."

Their acknowledgment lights winked on.

Will and Fred ran, weaving from side to side. Dr. Halsey clutched

onto Fred with one arm, and in her free hand she clutched the crystal. Fred's motion tracker showed dozen of targets behind them, then hundreds.

A pair of detonations thumped, an overpressure wave blurred his motion tracker, subsided, and then half of those contacts were gone.

Will and Fred ran into an arched passage set in the wall of the great room. Kelly crouched in the hallway and fired past them with her pistols.

Fred opened his COM. "SPARTAN-029. SPARTAN-039. Acknowledge." Static hissed through his speaker. Vinh's and Isaac's lights remained dark.

"Prep your det sack and seal this passage," Fred ordered Kelly.

Fred set down Dr. Halsey, turned, and bumped up his display's magnification.

Hundreds of Covenant Elites and Jackals poured from the grav shaft. They swarmed over the floor of the great chamber, a living tide as unstoppable as the ocean.

They weren't shooting anymore, though. Dr. Halsey was correct: They wanted the crystal she'd taken.

"Go!" Fred said. "Kelly, blow the hallway. Let's move."

Kelly hesitated a heartbeat; Fred saw her searching for Vinh and Isaac in the mass of Covenant. They weren't there; not alive anyway. Kelly dropped the olive-green satchel of high explosives. Will picked up Dr. Halsey, and they all ran deeper into the corridor.

Five seconds later the satchel detonated. A wave of acrid air washed up the hallway and choked the corridor with dust and smoke.

Kelly took the lead position, both pistols ready; she rounded a corner—and skidded to a halt. The passage was a dead end.