1750 Hours, September 22, 2552 (Military Calendar)

Aboard Unidentified Covenant Flagship,

Soell System, Halo Debris Field.

Plasma bolts impacted on the Longsword’s hull and splashed across the windshield. The packets of glowing energy sizzled across the cockpit and etched cloudy, molten trails into the glass.

A legion of Grunts hunkered behind docked Seraph fighters and fuel pods. Some darted in and out of cover and fired ghostly green bolts of plasma at the Longsword.

“I got ‘em,” Polaski said and flipped a switch.

The Longsword’s landing gear deployed and raised the craft a meter off the floor. “Guns clear,” Polaski announced. “ ‘Bye, boys.’ ”

She brought up a targeting reticle and swept it around the bay. A hail of 120mm rounds tore through the Grunts’ cover. Fuel pods and unshielded fighters detonated and sent metal fragments and alien soldiers hurtling to the deck. The air exploded into roiling flame, which billowed toward the ceiling and then subsided. Pools of burning fuel and the charred bodies of Grunts and Covenant Engineers littered the launch bay.

“Fire suppression system activating,” Cortana said.

Jets of gray mist blew down from above. The fires intensified for a moment, then guttered and went out.

“Is there atmosphere in the bay?” the Chief asked.

“Scanning,” Cortana replied. “Traces of ash, some contamination from the melted ship hulls, and a lot of smoke, but the air in the bay is breathable, Chief.”

“Good.” He turned to the others. “We’re going in. I’ll lead. Locklear, you’re up with me. Sergeant, you’ve got the rear.”

“You’ll need to take me, too,” Cortana said. “I’ve pulled a schematic of this ship to navigate, but the engineering controls have been manually locked down. I’ll need direct access to this ship’s command data systems.”

The Chief hesitated. His armor allowed an AI like Cortana to tag along stored in a special crystal layer. On Halo, Cortana had been an invaluable tactical asset.

Still, she also used part of his armor’s neural interface for processing purposes, literally harnessing parts of the Chief’s brain. And after coming out of Halo’s computer system, she’d been acting… twitchy.

He put his discomfort aside. If Cortana turned into a liability, he’d pull the plug.

“Stand by,” he said. He punched a key on the computer terminal and dumped Cortana to a data chip. A moment later the terminal pulsed green.

He removed the chip and slotted it in the back of his helmet. There was a moment of vertigo, and then the familiar mercury-and-ice sensation flooded his skull as Cortana interfaced.

“Still plenty of room in here, I see,” she said.

He ignored her customary quip and nodded at Johnson and Locklear. “Let’s go.”

Sergeant Johnson hit the door release, and the side hatch slid open. Locklear shouldered his rifle and poured fire through the opening. A pair of Grunts who had crouched near the Longsword to protect themselves from the fire flew backward onto the deck. Phosphorescent blood pooled beneath their prone forms.

The Chief dived through the open hatch and rolled to his feet; his motion tracker picked up three targets to his side. He whirled about and saw a trio of Covenant Engineers. He removed his finger from the weapon’s trigger. Engineers were no threat.

The odd, meter-high creatures hovered above the deck, using bladders of some lighter-than-air gas produced by their bodies. Their tentacles and feelers probed a tangle of fuel lines, quickly repairing the pipes and pumps.

“Funny that there’s no welcoming committee yet,” Cortana whispered. “I looked over this ship’s personnel roster: three thousand Covenant, mostly Engineers. There’s a light company of Grunts, and only a hundred Elites.”

“Only a hundred?” the Chief muttered.

He waved his team forward toward a heavy door at the back of the launch bay. The air was full of smoke and fire-suppressing mist, which reduced visibility to a dozen meters.

The rattle of assault rifle fire echoed through the bay. The Chief spun to his right and brought his own rifle to bear.

Locklear stood over the twitching corpses of the Engineers. He fired another burst into the fallen aliens.

“Don’t waste your ammunition, Corporal,” the Sergeant said. “They may be ugly, but they’re harmless.”

“They’re harmless now, Sarge,” Locklear replied. He wiped a spatter of alien blood from his cheek and smirked.

The Chief tended to agree with Locklear’s threat analysis of the Covenant: When in doubt, kill. Still, he found the young Marine’s actions unnecessary… and a little sloppy.

The architecture of the Covenant fighter bay was similar to the interior of the other Covenant ship the Chief had recently been inside, the Truth and Reconciliation. Low indirect lights illuminated the dark purple walls. The alien metal appeared to be stenciled with odd, faintly luminescent geometric patterns that overlapped each other. The ceiling was vaulted and unnecessarily high, maybe ten meters. In contrast to a human ship, it was a waste of space.

The Chief spotted a large door at the back of the bay.

The door was a distorted hexagonal shape and large enough that the entire team could enter at the same time—not that he’d ever be foolish enough to take up such a formation in hostile territory. The door had four sections that, when keyed to open, would silently slide away from the center.

“That will take us to the main corridor,” Cortana said. “And from there, to the bridge.”

The Chief waved Locklear to the right side of the door, Sergeant Johnson to the left.

“Lieutenant Haverson,” he called out, “you’re our rear guard. Polaski, hit the door controls. Hand signals from now on.”

Haverson tossed an ironic salute to the Chief but tightened his grip on his weapon and scanned the bay.

Polaski moved forward and crouched by the panel in the middle of the door. She turned her cap around and leaned closer, then looked back to the Chief and gave him a thumbs-up.

He raised his rifle and nodded, giving her the go-ahead to breach the door.

She reached for the controls. Before she touched them, though, the door slid apart.

Standing on the opposite side were five Elites: Two stood shielded by either edge of the door; a third stood centered in the corridor, plasma rifle leveled at the Chief; behind it, the fourth Elite covered the rear of their formation; and one last Elite crouched in front of the door control panel—nose to nose with Polaski.

The Chief fired two bursts directly over Polaski’s head. His first shots struck the Elite in the middle of the corridor. His second burst hit the Elite standing rear guard. The alien warriors hadn’t activated their shields, and 7.62mm rounds punctured their armor. The pair of Elites dropped to the deck.

Their comrades on either side of the door howled and attacked. The whine of plasma rifle fire echoed through the bay as blue-white energy bolts crashed into the Chief’s own shields.

His shield dropped away, and the insistent drone of a warning indicator pulsed in his helmet. His vision clouded from the flare of energy weapon discharges, and he struggled to draw a bead on the Elite in front of Polaski. It was no good—he had no clear shot.

The Elite drew a plasma pistol. Polaski drew her own sidearm.

She was faster—or luckier. Her pistol cleared its holster; she snapped it up and fired. The pistol boomed as a shot took the Elite right in the center of its elongated helmet.

The Elite’s own shot went wide and seared into the deck behind Polaski.

Polaski emptied her clip into the alien’s face. A pair of rounds rocked the alien back. Its shields faded, and the remaining rounds tore through armor and bone.

It fell on its back, twitched twice, and died.

Johnson and Locklear unleashed a hellish crossfire into the corridor and made short work of the remaining Elites as Polaski hugged the deckplates.

“Now that’s what I’m talkin’ about,” Johnson crowed. “An honest-to-God turkey shoot.”

Ten meters down the passage a dozen more Elites rounded a corner.

“Uh-oh,” Locklear muttered.

“Sergeant,” the Chief barked. “Door control!” John moved to Polaski’s position in two quick strides, grabbed her by her collar, and dragged her out of the line of fire. Plasma bolts singed the air where she’d been.

He dropped her, primed a grenade, and tossed it toward the rushing Elites.

The Sergeant fired his assault rife at the door controls; they exploded in a shower of sparks, and the doors slammed shut.

A dull thump echoed behind the thick metal, then an eerie silence descended on the bay. Polaski struggled to her feet and fed a fresh clip into her pistol. Her hands shook.

“Cortana,” the Chief said. “We need an alternate route to the bridge.”

A blue arrow flashed on his heads-up display. The Chief turned and spotted a hatch to his right. He pointed to the hatch and signaled his team to move, then ran to the hatch and touched the control panel.

The small door slid open to reveal a narrow corridor beyond, snaking into the darkness.

He didn’t like it. The corridor was too dark and too narrow—a perfect place for an ambush. He briefly considered heading back to the primary bay door, but abandoned that idea. Smoke and sparks poured from the door seams as the Covenant forces on the other side tried to burn their way through.

The Chief clicked on his low-light vision filters, and the darkness washed away into a grainy flood of fluorescent green. No contacts.

He paused to let his shields recharge, then dropped into a low crouch. He brought his rifle to bear and crept into the corridor.

The interior of the passage narrowed, and its smooth purple surface darkened. The Chief had to turn sideways to pass through.

“This looks like a service corridor for their Engineers,” Cortana said. “Their Elite warriors will have a tough time following us.”

The Chief grunted an acknowledgment as he eased his way through. There was a scraping sound and a flash of sparks as his energy shield brushed the wall. It was too tight a fit. He powered down the shields, which left him just enough room to squeeze through.

Locklear followed behind him, then Polaski, the Sergeant, and finally Haverson.

The Chief pointed at Haverson, then at the door. The Lieutenant frowned, then nodded. Haverson closed the hatch and ripped out the circuitry for the control mechanism.

There had been dozens of Engineers in the launch bay—and there were enough on the ship to merit their own access tunnel. The Chief hadn’t seen anything like this on the Truth and Reconciliation.

In fact, he hadn’t seen a single Engineer on that ship. What made this ship different? It was armed like a ship of war… yet had the support staff of a refit vessel.

“Stop here,” Cortana said.

The Chief halted and killed his external speakers so he could speak freely. “Problem?”

“No. A lucky break, maybe. Look to your left and down twenty centimeters.”

The Chief squinted and noticed that a portion of the wall extruded into a circular opening no larger than the tip of his thumb. “That’s a data port… or what passes for one with the Covenant Engineers. I’m picking up handshake signals in short-wave and infrared from it. Remove me and slot me in.”

“Are you sure?”

“I can’t do much good in there with you. Once I’m directly in contact with the ship’s battlenet, however, I can infiltrate and take over their systems. You’ll still need to get to the bridge and manually give me access to their engineering systems. In the meantime, I may be able to control secondary systems and buy you some time.”

“If you’re sure.”

“When have I not been sure?” she snapped.

The Chief could sense her impatience through the neural interface.

He removed Cortana’s data chip from the socket in his helmet. The Chief felt her leave his mind, felt the heat rush back into his head, pulsing with the rhythm of his heart… and once again, he was alone in the armor.

He slotted Cortana’s chip into the Covenant data port.

Locklear’s face rippled with disgust, and he whispered, “You couldn’t pay me to stick any part of myself in that thing.”

The Chief made a slashing gesture across his throat, and the Marine fell silent.

“I’m in,” Cortana said.

“How is it?” the Chief said.

There was a half-second pause. “It’s… different,” Cortana replied. “Proceed thirty meters down this passage and turn left.”

The Chief motioned the team forward.

“It’s very different,” Cortana murmured.

Cortana was built for software intrusion. She had been programmed with every dirty trick and code-breaking algorithm the Office of Naval Intelligence, Section Three had ever created, and a few more tricks she’d developed on her own. She was the ultimate thief and electronic spy. She slipped into the Covenant system.

It was easy the first time she had entered their network as the Longsword had approached the flagship. She had set their weapons systems into a diagnostic mode. The Covenant had determined the problem and quickly reset the system, but it had given Polaski the precious seconds her sluggish human reflexes had needed to get inside the launch bay.

“How is it?” the Chief asked.

Now the element of surprise was gone, and the system’s counterintrusion systems were running on high alert. Something else prowled the systems now. Delicate pings bounced off the edges of Cortana’s presence; they probed, and withdrew.

It felt as if there were someone else running through their system. A Covenant AI? The possibility of one nearby intrigued her.

“It’s… different,” she finally answered.

She scanned the ship’s schematics, deck by deck, then flashed through the vessel’s three thousand surveillance systems. She picked out the quickest route to the bridge from their current position and stored it in a stolen tertiary system buffer. She multitasked a portion of herself and continued to analyze the ship’s structure and subsystems.

“Proceed thirty meters down this passage and turn left.”

Cortana hijacked the external ship cameras and detected the six Covenant cruisers. They had stalled their pursuit of the Longsword and now hovered a hundred kilometers off the flagship’s starboard side. The strange U-shaped Covenant dropships launched from the cruisers and swarmed toward the flagship. That was trouble.

Within the flagship she spotted a dozen Elite hunter-killer teams sweeping the corridors. She scrambled the ship’s tracking systems, generated electronic ghosts of the Chief and his team along a path directed toward the nose of the ship, where UNSC command-and-control centers were typically located. Maybe she could fool the Elites into a wild goose chase.

She uploaded the coordinates of those enemies into the Chief’s HUD.

A tickle of feedback teased through the data stream.

Cortana locked onto the source of that feedback, listened, discerned a nonrandom pattern to the signal, then cut off contact. She had no time to play hide-and-seek with whatever else was in this system.

Cortana had to finally admit to herself that she didn’t have the power to contend with a possible enemy artificial construct. She had absorbed a tremendous volume of data from Halo’s systems: eons’ worth of records on Halo’s engineering and maintenance, the xenobiology of the Flood, and every scrap of information on the mysterious “Forerunners” the Covenant revered so much. The information would take her a week of nonstop processing to examine, collate, codify… let alone understand.

Even compressed, all the data filled her and cut into optical subsystems that she usually reserved for her processing. She had a nagging suspicion that the file compression had been too hasty—and that the Halo data might be corrupted.

In effect, the vast amount of information she had copied bloated her, made her slower and less effective.

She hadn’t mentioned this to the Chief. She could barely admit it to herself. Cortana was extremely proud of her intellect. But to operate as if nothing were different would be even more foolish.

She sent a blocking countersignal along the connection where this “other” was trying to contact her.

The portion of her consciousness examining the ship’s structure discovered that the bridge had another access point. Stupid. She should have seen it immediately, but this other entrance had been filed under the schematics as an emergency system. It was a tiny corridor that connected to a set of escape pods. That route shared a vent with an engineering passage.

“Chief, there’s another way to the bridge.”

“Affirmative. Wait one.” There was a burst of gunfire on the COM, then silence. “Go ahead, Cortana.”

“Uploading the route now,” she said. “I do not believe you can fit through this new passage in your armor. I suggest you split your team and proceed along both routes to maximize your chances of egress onto the bridge.”

“Understood,” the Chief said. “Polaski and Haverson with me. Johnson and Locklear, you take the escape pod route.”

She continued to track both teams and the relative positions of the Covenant parties. She replicated additional ghost signals to confuse the enemy.

Cortana picked up increasing communications bandwidth between the flagship and the cruisers. Reports of the invaders—a call for help—a warning to be relayed to the home world. There were references to the “holy one,” and those messages had what she considered amusing attempts at encryption to keep them secret. Curious, she had to investigate what the Covenant thought important enough to hide.

As she decrypted those messages and others cross-referenced and filed in their COM archives, she detected an energy spike on the flagship’s lateral sensors. One cruiser off to starboard moved farther away; it turned, its engines glowed, the black around it rippled electric blue. The Covenant ship sped forward, tore the night, and vanished into Slipspace.

Cortana noted their departure vector for future reference… a possible clue at the location of their home world.

It was puzzling that the Covenant would call for help. Their warriors were intensely proud; they almost never ran from a fight. They didn’t ask for help… not for themselves. Then again, this ship, although armed for war, didn’t appear to be staffed for combat. It carried only a few hundred Elites and an army of Engineers.

As Cortana pondered this, she continued to generate a countersignal to match to the probe sent by the other presence in the system. She hoped to cloak her activity as long as possible. The other’s signal morphed into a series of Bessel functions, and she compensated to match.

She automated this process, commandeering a portion of the Covenant’s own NAV computer to do so, and then she herded the electronic ghosts of the Chief and the others to confuse the pursuing Elite forces.

At the same time, she continued her study of the Covenant ship and its systems—it was a unique opportunity. The information on their advanced Slipspace drive, their weapons—it could leapfrog human technology decades forward.

“Cortana?” The Chief’s voice broke her concentration. There were sounds of plasma bolts and automatic weapons fire. “We’ve got Elites in active camouflage in the passage. We need a way around this intersection.”

She had not considered the Elites’ light-bending technology. She was doing too much, spreading herself too thin. She halted her ongoing study of the Covenant technology and found the Chief a way around the intersection.

She rebooted her human communications and protocol routines and said, “Access panel to your right, Chief. Down three meters, straight ahead five meters, turn to your left and then up again.”

She heard an explosion. “Got it,” the Chief said.

Cortana had to focus on protecting the Chief. She halted her other searches and scrutinized the ship’s schematics. There had to be something she could use. A weapon. A way to stop their enemies—there: the backup terminus for their atmospheric preprocessors. Unlike the other systems, this one was classified as low priority and had minimal security layers.

She generated several hundred thousand Covenant codes in a microsecond and cracked the system. She diverted the air vents along the corridors the Chief and his team occupied to the primary air systems. She then tasked the processor pumps to service the rest of the ship and activated them—in reverse.

Warnings flashed throughout the Covenant system as the pressure suddenly dropped in 87 percent of the ship’s passages. She squelched them.

The other presence in the system tried to shut the pumps off. She blocked that signal and assigned a new code to the security systems: “WE REGRET TO INFORM YOU.”

She heard the other AI scream, an echo of an echo that reverberated through her processors. She knew the sound—familiar like a human voice, but terribly distorted.

She scanned through the ship’s cameras and saw Grunts squeal and fall over, methane leaking from their breathers as the pressure dropped. Engineers turned blue, slowed, and died, floating in place with tentacles twitching, still searching for something to fix. The Elite hunt-and-destroy parties halted in the corridors and clutched their throats, mandibles snapping at air that was no longer there; they toppled and suffocated.

An impulse flickered through her ethics subroutine and generated an interrupt command, designed to make her stop and rethink her decisions. But Cortana knew it was either kill or be killed. She rerouted all signals from her ethics routine and shut it down. She couldn’t afford to be slowed down by such secondary considerations.

“Chief,” she whispered over the COM. “Be advised that the passages I’m uploading into your NAV system no longer contain atmosphere. Proceeding into those regions will be lethal to the rest of your team.”

There was a three-second pause, and then the Chief replied, “Understood.”

Cortana’s decryption of the Covenant communiqués referencing the “holy one” finally cycled to a halt. The language in them was unusually ornate—even more so than the florid prose of the higher-ranking Elites. It was impossible to develop a literal translation, but she gleaned that some dignitary was due at the Halo construct. Soon.

This visitor was so important that these warships were only the advance scouting party. More ships were on their way. Hundreds of them.

“Chief,” Cortana said. “We may have a prob—”

“Hold transmission, Cortana,” the Chief interrupted. “We’re outside the command center. Can you tell how many are inside?”

“Negative. They have disabled the bridge sensors,” she replied.

“You heard Cortana,” the Chief said, addressing his companions. “Expect anything. Sergeant, you and Locklear: Get in position.”

“Roger that,” Sergeant Johnson whispered. “In position and ready to kick Covenant ass.”

“We’re about to blow the door on this end, Cortana. Stand by.”

Cortana picked up energy surges on the flagship’s lateral sensors. The Covenant cruisers turned; their plasma weapons warmed and readied to fire.

“Chief,” Cortana said. “Hurry!”

“Plasma grenades on my mark,” the Chief said on the COM. “Mark! Toss them and take cover.”

The Chief tossed two plasma grenades. They burned magnesium-brilliant and adhered to the heavy alloy of the bulkhead doors that encased the bridge—one of the alien weapon’s more useful properties. He moved around the corner of the passage and shielded Haverson and Polaski.

Five seconds elapsed, and a flash filled the hallway. The Chief moved back to the doors. They shone mirror-bright where the grenade had detonated but were otherwise unharmed.

A hundred grenades wouldn’t have blasted through these doors—but when Covenant plasma grenades detonated, they disrupted electronics and shielding. The Chief dug his gauntleted fingers into the door crack—hoping that the disruption had knocked out the motors and shielding keeping these doors closed.

He braced himself and tried to pull the doors apart at the seams. They slid a few centimeters, then ground to a halt. The Chief adjusted his footing and strained at them again, but the doors remained frozen in place.

The Chief’s motion sensors pulsed a warning—there was movement directly on the other side of the door.

He shoved the muzzle of his assault rifle into the narrow opening and squeezed the trigger. Spent shell casings clattered to the floor.

A howl echoed from the other side, and a curl of gray smoke drifted through the crack.

The Chief slung his rifle, grabbed the doors, flexed, pulled—and this time the heavy metal moved.

A flash of plasma fire washed over his shields, blinding him. He ignored it, closed his eyes, and continued to force his way through the door. Another plasma shot struck him in the chest.

The doors were half a meter apart—good enough.

He rolled to the side and gave his shields a moment to regenerate.

Nothing. The suit’s alarms pulsed insistently. He squinted through the glowing spots that swam in his vision and scanned the damage report—the MJOLNIR’s internal temperature was over sixty degrees Celsius, and the Chief heard the whine of microcompressors in his armor, trying to compensate.

“Marines!” he yelled. “Suppressing fire!”

“Hell yes, Master Chief,” Locklear replied. Locklear dropped to one knee and fired through the opening; Johnson stood and fired over the younger Marine’s head.

The Chief rebooted his shielding control software.

Nothing. His shield system was dead.

The shooting stopped. “I’m out,” Locklear said.

“And I’m in,” the Chief said.

He rushed into the room and stepped over the dead Elite on the floor before him. Its torso had been ripped open—shot as it tried to hold the doors closed.

The Chief scanned the room. It was circular, twenty meters across, with a raised platform in the center that was ten meters across and ringed with holographic control surfaces. The central platform floated over a pit in the floor. Within the pit were exploded optical conduits and a trio of Covenant Engineers, cowering in fear.

“Don’t shoot the Engineers,” Cortana warned. “We need them.”

“Understood,” the Chief replied. “Acknowledge that order, Locklear.”

There was a pause over the COM and then Locklear said, “Roger.”

Along the circular walls, floor-to-ceiling displays showed the flagship’s status as a variety of charts and graphs, peppered with the odd calligraphy of the Covenant. They also showed the space surrounding them, and the five remaining Covenant cruisers closing in.

The Chief caught a motion in his peripheral vision: An Elite in jet-black armor materialized from the wall display, its light-bending camouflage dissolving. It strode toward the Chief, roaring a challenge.

The Chief’s rifle snapped up, and he squeezed the trigger. Three rounds spat from the muzzle, then the bolt locked open. The ammo counter read 00—empty.

The shots flared on the Elite’s shielding; a lucky round penetrated and deformed its shoulder. Purple-black blood spattered on the deck, but it shrugged off the wound and kept coming.

Haverson charged into the room and leveled his pistol. “Hold it!” he yelled, and thumbed off the weapon’s safety.

The Elite drew a plasma pistol and fired at the Lieutenant—but never took its eyes off the Chief.

Haverson cursed and scrambled out of the room as the plasma charge slashed at him.

The Chief altered his grip on the rifle and crouched in a low fighting stance. Even with the shield malfunction, he was confident he could take a single Elite.

The Elite removed its helmet and dropped it. The plasma pistol clattered to the deck a moment later. It leaned forward, and its mandibles parted in what the Chief guessed had to be a smile. It moved closer, and a blue-white blade of energy flashed to life in its hands.

The Elite raised the energy blade and charged.