The Advanced Systems chamber was a killing box.
Steel walkways crisscrossed above humming conduits, the air thick with ionized heat and the constant thrum of overloaded generators. Red emergency lights strobed against white Institute walls, painting everything in pulses of warning and blood.
The moment Nate and the Minutemen breached the doorway, the room erupted.
Synths poured from maintenance alcoves and ceiling hatches—Gen 2 frames clanking forward with precision rifles, Gen 3 units darting between cover, laser fire filling the space in blinding sheets. Turrets unfolded from recessed panels, barrels swiveling down.
"Take cover!" Preston shouted as a beam scorched the railing inches from his head.
Minutemen returned fire from behind consoles and coolant tanks, rifles barking, grenades detonating in sharp concussions that rattled the floor plates. A young militia member rushed forward to flank—only to be cut down mid-stride by a synchronized volley. He dropped without a sound.
"Medic—!" someone yelled, too late.
Nate pushed ahead anyway, combat rifle kicking against his shoulder as he cleared a path meter by meter. The Institute fought like it always had—efficient, relentless, uncaring. Every step forward cost blood.
Then the room shifted.
Heavy footfalls echoed from the far end as the forcefield guarding the reactor access flared brighter, stabilizing.
Two figures emerged through the haze, emerge as synth with respected labels in their shoulder.
Z4K-97B moved first—towering, plated in reinforced synth armor, a rotary cannon mounted directly to its arm. Its optics glowed a hostile red as it spun up, minigun roaring to life.
Beside it strode A-2018—leaner, faster, carrying a prototype plasma caster that hummed with unstable power, arcs of violet energy crawling along its barrel.
"SHIT! They look like Elite units!" Preston shouted. "They weren't shut down!"
Z4K-97B answered with gunfire.
The minigun tore through cover like paper. A barricade vanished in a cloud of sparks and shrapnel, taking two Minutemen with it. Bodies hit the deck hard, unmoving.
"Fall back—spread out!" Nate ordered, diving behind a reactor console as plasma scorched the air above him.
A-2018 advanced with terrifying calm, firing controlled bursts that melted armor and flesh alike. A Minuteman lunged forward with a frag grenade—Z4K backhanded him mid-throw, crushing him against the floor before the grenade detonated uselessly behind the synth.
The cost mounted fast.
Nate popped up, firing burst after burst into Z4K's joints, rounds sparking uselessly off reinforced plating. Preston flanked, launching a missile that slammed into A-2018's chest—
—but the synth stayed upright, armor blackened but intact.
"Password carriers," Preston gasped. "They're guarding the reactor terminal!"
Z4K charged.
Nate didn't get out of the way in time.
The synth slammed into him like a freight train, hurling him across the walkway. He hit the deck hard, breath driven from his lungs, pain exploding through his ribs. His Pip-Boy screamed warnings.
Preston rushed to cover him—only to take a plasma bolt to the shoulder, spinning him down in a heap.
"Nate—!" Preston groaned, clutching his arm.
Z4K raised its cannon for the kill.
A surviving Minuteman tackled the synth from behind, jamming a pulse grenade into its back.
"FOR THE COMMONWEALTH—!"
The grenade detonated.
Z4K-97B staggered, systems stuttering just long enough for Nate—bloodied, half-blind—to drag himself upright and empty his magazine point-blank into the exposed core.
The synth collapsed in a heap of molten metal.
A-2018 screamed—an electronic shriek—as it charged, plasma weapon overheating.
Preston, teeth clenched through the pain, braced himself and fired one last shot straight into the weapon's emitter.
The caster detonated.
A-2018 vanished in a white-hot explosion that rocked the chamber, throwing both men to the ground.
Silence followed—broken only by the hiss of cooling metal and labored breathing.
Nate dragged himself to his feet, limping, and approached the reactor console. Two access keys lay amid the wreckage.
He inserted them.
The forcefield dropped.
And reality broke.
Beyond the barrier, the reactor chamber pulsed with something impossible—not nuclear fire, not fusion—but a contained singularity.
Blackhole energy.
Space bent subtly around it, light warping, sound feeling wrong. Sangvis Ferri research signatures flickered across the terminal—experiments no one in the Institute had ever fully understood, let alone controlled.
"…What the hell is that," Preston whispered.
Nate keyed his radio with shaking fingers.
"Sarah. We've got a problem."
Static—then her voice, sharp despite exhaustion.
"Talk to me."
"It's not a normal reactor," Nate said. "It's some kind of… singularity tech. Sangvis Ferri. We didn't expect this."
A pause.
Then Sarah's tone hardened.
"Mayling. Now."
Mayling's voice cut in immediately. "I see it. That's not sustainable containment."
Sarah didn't hesitate.
"Is the pulse charge Sturges gave us enough to bring this place down?"
A rapid burst of typing echoed over the channel.
"Yes," Mayling answered. "But it needs adjustment. I'm transmitting the parameters now."
Nate's Pip-Boy chimed.
Data streamed in.
"Your Pip-Boy can tune the charge on the fly," Mayling continued. "You'll need to plant it close. Once it goes, this whole place will collapse inward."
Nate stared at the impossible reactor—at the heart of the Institute, beating wrong.
"…Understood," he said.
He looked at Preston, battered but alive.
"One last run," Nate said.
Preston forced a grim smile. "Wouldn't miss it."
The Institute's Relay control room, once a nexus of cold efficiency, now bore the scars of intrusion—scorch marks blackening the white walls, consoles flickering with error codes from the overridden systems, the red emergency lights dimming to a sullen glow as the facility's power diverted to failing defenses. The air hung heavy with the acrid scent of burned circuitry and the faint, sterile tang of recycled oxygen, a reminder that this underground empire was crumbling. Nate, Preston, and the remaining Minutemen—four weary survivors now, their blue coats torn and bloodied—stumbled back into the room, boots echoing on the grated floor. They had run their way up from the lower levels, without hinderence from power downed synths, but exhaustion etched their faces like radiation burns.
Sturges looked up from the console, his grease-stained hands pausing mid-keystroke, holographic displays casting blue shadows across his weathered features.
Mayling, her brown hair in high ponytails still damp from the tunnels, golden eyes sharp behind red-tinted goggles, shouldered her massive toolbox with a clank. "I'm heading back," she said, stepping onto the relay pad. "Gotta make sure those Institute civilians keep in line on Spectacle Island. Can't have them causing trouble while we're wrapping up here." The pad hummed to life, blue energy enveloping her in a swirl—toolbox, white shirt under gray vest, black shorts, and all. In a flash, she was gone, teleported to the island's secure holding areas.
The Brotherhood had already departed en masse, their power-armored forms vanishing in coordinated beams back to their bases, leaving only Elder Arthur Maxson and two elite guards.
Elder Maxson look at Sarah before his turn to teleport: "I'll shall await you in tallest building roof"
They then teleport to the rooftop of the Mass Fusion building—the tallest spire in the ruins, its skeletal frame piercing the night sky—awaiting Nate's party from their vantage point.
Nate wiped sweat from his brow, his vault suit scuffed and torn, turning to Sarah and Team 404—UMP45, UMP9, HK416, and G11 standing like silent sentinels, their black tactical gear still pristine despite the grime. "So it's just us left," he said, voice rough with fatigue. "Sturges, let's teleport out of here. We've done what we came for."
Sturges straightened, but his expression was grim, fingers hovering over the controls. "Would love to, General, but we have a situation." He pointed toward the corner of the room, where a small figure had emerged from the shadows—a boy, no older than ten, clad in a crisp white Institute uniform, the label "S9-23" embroidered on his left chest like a serial number. His face was pale, eyes wide with a mix of fear and determination, hair neatly combed in a way that screamed artificial perfection which same boy in first encounter when nate found him.
The boy stepped forward, his voice small but steady. "Please don't leave here, Dad."
Nate froze, his combat rifle slipping slightly in his grip, eyes widening in denial. "Who told you that you're my son?" he demanded, the words sharp, laced with a raw edge of pain and disbelief.
Sarah's voice cut in softly but firmly. "Nate..."
The boy—young Shaun—tilted his head, unfazed. "Nobody. It just... is as it is."
Nate's face twisted, the weight of the Institute's deceptions crashing down anew. "You're NOT my....."
"STOP!" Sarah interjected, her tone like a whipcrack, stepping between them with her M590 shotgun still in hand. "This is not the time or place. Sturges, teleport this child to the Castle—we'll sort it out later. Teleport 416 and G11 with the boy. Keep him secure."
Sturges nodded quickly, fingers dancing over the console. "Ok, Commander. Teleporting the kid to the Castle now." The relay pad hummed, blue energy enveloping young Shaun, HK416, and G11—the Dolls flanking the boy protectively, their expressions neutral but optics watchful. In a flash, they vanished, leaving the room quieter, the alarms a distant wail.
Nate stared at the empty pad, his shoulders slumping slightly, the revelation hanging like a spectras. Sarah placed a hand on his arm briefly. "We'll figure it out, Nate. But right now, focus the mission."
He nodded slowly, holstering his weapon. "Yeah... let's get out of here."
Sturges gave a tight nod. "Relay's stable. Whenever you're ready."
Nate didn't answer right away. He took one last look at the platform—the humming coils, the scorched floor, the place where a child had stood and called him dad. Then he stepped forward.
White light swallowed the world.
Wind hit him first.
Cold, high-altitude air whipping across the rooftop of the Mass Fusion building. The city sprawled below—ruined, scarred, alive. One by one, figures resolved around him as the relay discharged its last pulse: Sarah, her armor battered and blackened; UMP9 and UMP45 flanking her instinctively; Preston and the surviving Minutemen, soot-streaked but standing; Sturges rubbing his temples, relief written all over his face.
Power armor servos whined nearby.
Elder Arthur Maxson stood at the edge of the roof without his power armor, his coat snapping in the wind, with two Knights at his back. He turned as the last teleport flare faded.
"I'm glad to see you all made it out," Maxson said, voice carrying easily over the wind. "Your Objective achieved. My men have already placed the detonator. With the Frequency matched exactly to what your Minutemen engineer provided."
He stepped forward and held out the device.
A heavy, utilitarian block of metal. One oversized red button. No ceremony. No flourish. Just finality.
Maxson extended it toward Sarah.
For a moment, it seemed natural—expected—that it would be hers.
But Sarah didn't take it.
She looked at the detonator, then at Nate. Her expression softened, stripped of command and fury and strategy, leaving only something painfully human.
She gently pushed Maxson's hand aside—and placed the detonator into Nate's palm.
"I'm sorry," she said quietly, so only he could hear. "I won't push this weight onto you any harder than it already is. This one… is yours."
The device felt heavier than it should have.
Maxson inclined his head toward Nate, solemn rather than triumphant. "Press that button, and you don't just destroy an enemy. You end a shadow that's poisoned the Commonwealth for generations. You restore order. You give people a future without fear."
He took a step back, giving Nate space.
"It's time," Maxson said."General of the Minutemen."
The wind howled.
Below them, somewhere beneath concrete and steel and centuries of buried ambition, the Institute waited.
Nate stared at the red button.
This started with a siren.A vault door.A child taken from his arms.
He thought of Sanctuary—broken houses and stubborn hope.Of Preston's voice on the radio, refusing to give up.Of Minutemen standing their ground at the Castle.Of Sarah bleeding, laughing, still fighting.Of Shaun—Father—lying in a bed of impossible machines, choosing legacy over life.
And of the boy in white.
Am I destroying monsters… or burying my own past?
His thumb hovered over the button.
They said this place was humanity's future.But a future built on kidnapping, replacement, fear…it isn't a future.
He exhaled slowly.
"For the Commonwealth," Nate said—not loudly, but with certainty.
He pressed the button.
For a heartbeat, nothing happened.
Then the ground trembled.
Far below, light erupted—contained at first, then blooming outward as the Institute's reactor collapsed in on itself. A deep, thunderous roar rolled across Boston, followed by a column of blinding energy punching skyward before imploding into itself.
The city shook.
Windows rattled miles away.
A hollow silence followed—heavy, final.
Sarah closed her eyes.
Preston removed his hat, clutching it to his chest.
Maxson watched without flinching, jaw set, as history burned itself out beneath the earth.
Nate lowered his hand, the detonator suddenly become lifeless metal.
It was done.
The Institute was finally gone.