Work Header

The Sum of Our Sin(x)

Chapter Text

Praise was not something that came easily in the Shen household. Even at Caltech, while monitoring graduate students and their achievements, Dad would only pass a, “good work”, and “the procedures are sound. Continue,” to his best students. Even to Lily – his flesh and blood, and only living family – she rarely heard a single, “I’m proud of you.” Too late for that now: Dr. Shen - dad - sleeps under a coverlet of ferns and boulders, and Lily will never see him again. She will never have the opportunity to ask him questions about a city swathed in smog, or compare designs, or even share another bowl of chopped up ian-chhiâng in glutinous rice. All that died with the old world.

Lily wonders what made him change. The way he spoke of the Commander painted a god in mortal flesh, a sword made human, and first and foremost, a leader.

As she extricates the Commander from the prison of the red space suit, Lily doesn’t see any of her father’s praise in the frail woman before her. The Commander has curled into the fetal position, her breaths shallow, arms dangling lifelessly over the side of the gurney. It isn’t a wraith-like Zhuge Liang that Lily wheels up to the Commander’s Quarters. For all of Dad’s tales of strength and poise, the Commander more closely resembles one of those battered women Hollywood loves to rescue from triads on the silver screen.

Lily shakes her head. Dad never said anything unless he meant it.

“You knew what you were doing, dad,” she later mumbles in the privacy of Engineering. Her wrench creaks as she brings ROV-R’s battered shell back together. “I just wish I was half as confident as you. Okay… reworked your repulsors with some of the parts I salvaged from your old engine.”

She tightens a bolt, trying to banish her doubts from her mind. Today, through terrible tactical advice, she had killed Osei and Ramirez. Would the Commander really do better? Had all those deaths been in vain?

“Should fix that stabilization problem you had.” Lily grips her GREMLIN’s carapace, willing the machine to come to life. “Come on, ROV-R. It’ll work.”

Slowly, ROV-R’s engines hum. The GREMLIN takes off, buzzing right towards the Commander standing at the mouth of Engineering.

“Dr. Shen.” The Commander sidesteps the flying robot. “What do I need to know?”

Old wounds rip open as Lily explains that no, Doctor Shen is dead, and Lily’s doctoral title is honorific at best, and the Avenger is all that remains of Doctor Shen’s legacy. She tells the Commander that she will do her best in his place, and tries to quell the disappointment in her voice. With his sixty years worth of engineering experience, Dad would have known better. She can only follow in his steps.

The Commander looks down.  “I’m sorry for your loss. From what Central has told me, your father would be proud of what you’ve accomplished.”

Lily bites her tongue – did this woman even watch the tapes of Operation Gatecrasher? But there’s no reason to complain now. She opens up her toolbox. “New orders, Commander?”

“Any concerns that you’d like addressed?” the Commander asks.

The Chief Engineer restrains a groan. The Commander is one of those women – a lady with a Messiah complex who thinks they can solve everybody’s problems. She had enough of those women, having met those overeager freshmen and grad students while visiting Dad's office at Caltech.

“Can we keep to engineering, sir?”

If I wanted a counselor, I’d do a Central and start drowning myself in alcohol. Then again, I inherited Dad’s alcohol tolerance… and I need to fix the ship if Central ends up crashing it.

XCOM’s newest superior smiles, barely perturbed by Lily’s abruptness. “Weapons, armor, medkits… I’ve been out of the loop since 2015. I’m afraid you’ll have to fill me in our capabilities.”

Thousands of projects dance before Lily’s eyes: appropriating ADVENT’s armor into their own, moving beyond ballistics, better plumbing systems so the soldiers’ locker room doesn’t perpetually smell of damp…

Lily thinks of Ramirez and Osei, bleeding out on foreign streets. ADVENT must be parading their corpses around the city centers by now. The aliens have no shame, seamlessly incorporating fallen rebels into their spiel of innocent civilians slaughtered by XCOM.

“A medkit would help us keep soldiers alive.” Lily motions to ROV-R. The implant in her hand generates signals that bring the GREMLIN over. A similar implant helps Central fly the ship. “We don’t have the resources to keep up. Armor’s best, but we can’t build any until we steal it off ADVENT.”

“If we could kill the enemy before they reach us,” the Commander says mildly, “that would further reduce casualties. Are we lacking for resources?”

Lily shifts from foot to foot, eager for the conversation to end. “If we can haul back some corpses, we’ll be good to go.” Lily explains the rest of the medkit’s benefits. The Commander orders a set of three, and then the AI summons her to the Bridge.

“I look forward to working with you, Chief Shen,” the Commander says.

Once the other woman’s footsteps have faded away, Lily slumps against her workbench. She fiddles with the touchscreen of her tablet.

ROV-R nudges her shoulder, and beeps sadly.

"I'm not running away," she tells her best friend. "I'm not going to think about Dad. I'm going to do the best job. I will be the Engineer XCOM needs."

Her voice bounces around the Engineering bay, as if her echo is trying to convince her.



The Avenger doesn’t feel like home, not when it is stained with Dad’s blood. The expeditionary team had colonized the ship’s upper levels, even bent most of the systems to their will. Lily had helped storm the alien ship’s lower levels, only to meet the skeleton crew who had been recently freed from cryostasis. The Sectoids began to merge minds with Dad – she shot them, but the breaking of the psionic link might had sealed Dad’s fate. She’s heard Central’s tales, of Sectoids who merged minds with a comrade, only to die once XCOM shot the initiator.

Dad died in sublevel 2, room B. The Commander has ordered sublevel 1, room B cleared, to make way for the Guerilla Training School. It is the last of rooms on that sublevel to be cleared.

Sooner or later, she must descend into the room where Dad died.

“Work is progressing well, sir,” she hears the recently acquired engineer, Howell, talk over the shriek of grinding metal. “We’ll be able to move to sublevel 2, room B and build the power relay there.”

“I look forward to it.” The Commander hesitates. “Central, why does everyone avoid that room?”

Central is slow to reply. “Dr. Shen was attacked there,” he says finally. “Sectoid got its psionic claws on him. He wasted away. Lily doesn't like to talk about it.”

“I’d imagine not. There’s no memorial for Shen up on the Wall.”

“No,” Central admits. “We always thought the Avenger was memorial enough. It was his life’s work.”

“I see. Well, please dedicate the supplies acquired from this room to the construction of the power relay,” the Commander says. “Howell, if I may speak to you in private?”




Lily finally enters room B, sublevel 2 when the Elerium generator is crafted. She does the final checks – chamber is sealed, heat vents safely into the insulated spaces, nothing looks ready to blow up… It looks nothing like the room which finally killed Dad.

ROV-R suddenly chirrups and directs her attention to the corner of the room.

The silhouette of the original Skyranger is stamped into the wall. is tooled into the wall below the memorial.

“…We didn’t forget him,” she tells ROV-R. “But I wish he was still here.”




"Hey, Chief Shen!" Howell shouts. The Engineer skids to a stop beside Lily's workbench. "You never eat dinner with us grunts. Why don't you join us?"

Lily spoons a bit of the watery gruel with stale oats from God-knows-where into her mouth, then sets the wrench onto her table. "I'm busy. You should be working on the Gauss rifle."

"Right, boss…" Howell looks at the table. "But maybe you shouldn't eat in Engineering."

Lily looks again at her bench. A grease-slicked wrench, oats sliding off its length, sits next to the barrel of the Gauss prototype.

The Chief Engineer groans. "How long have I been doing that?"

"Since I walked into the room." Howell takes out her handkerchief and begins to wipe the wrench. "I hope this stuff isn't toxic. There's a mess hall for a reason."

Lily pushes her bowl away. "I'll eat later," she says. "Thanks for telling me."

Howell frowns, but she takes up the bowl and leaves without another word.


About an hour later, Central intrudes on the safety of the Engineering Bay to demand updates on the rifle. At least, that's what she thought he would do.

"Eat," he says, throwing a ration bar at her. ROV-R flies forward to intercept the edible missile, then nimbly drops it in one of Shen's pockets. "Before you pass out."

Howell is a goddamn snitch, Lily thinks.

"Thanks, Dad," she scowls, and then freezes.

She's thirty-five, but age hasn't prepared her at all for the loss of her dad.

Central looks equally unsure. He runs a hand through his hair. "Look, Shen… we all miss your Dad. But you've got to take care of yourself. I… don't know what to say."

"I'll eat. Thanks." She looks at the Gauss Rifle in her hands, then at the ration bar. Her stomach is grumbling…

"The Mess Hall's clear," the Commander adds, appearing at Central's shoulder. XCOM's newest commanding officer looks Shen up and down. "There's still some food left," she adds, tone measured and careful. "I'd like to hear your opinion on our weaponry soon. Central thinks we should go for lasers right after Gauss. We'll see you soon."

"Our soldiers can hardly shoot straight," Central protests as the Commander drags him away. Is it just the light, or is he reddening? "You can't miss with a laser–"


Shen looks at the empty Engineering bay and the newly cleaned wrenches on her desk. She decides to eat before she does something dumb à la Central.




“Good shooting, Tex,” Central says as she lowers the newly crafted Gauss rifle. “You sure taught that cardboard a lesson.”

“It’s the edge we need,” the Commander says. “Even Doctor Shen and Vahlen couldn’t get us past ballistics. Are these ready to deploy, Chief Shen?”

“More than ready.” Lily flicks the safety on, and sets the rifle on the rack. She hands Central a fresh rifle. “You take a crack at it, Central. See how it compares to that bloated monstrosity you call a gun.”

“It’s the best gun XCOM has, Shen,” Central shoots back. There’s no venom in his voice, only the ease between two comrades. Lily has rarely seen him so calm; Bradford is a bitter drunk on the best of days. Dad told her about a time when Bradford would have been right at home in a Boy Scout troop. She can almost see the same man of Dad's stories before her, weighing the Gauss rifle in his hands. “Unless this knocks it out of the park.”

He lines up his sights with the cardboard Sectoid at the back of the room. Lily imagines the current running through the coils within the gun. She thinks of the diagrams Dad would draw as she complained about homework on Lenz’s law. Currents in coils generate magnetic fields. It seems so simple in theory. But to bring it to life, and put it in a soldier’s hands, is a different matter entirely.

For a brief second, she considers telling Central to drop the gun. Put it down, before it explodes and kills him. She has done thousands of tests to make the gun as stable as possible, but there is always human error, and Lily does not want to be the death of another man.

Central fires. The head, neck and torso of the Sectoid explode into fine black ash and charred paper.

“Knocks mine right out of the league,” the Central Officer says. “Good work.”

“This will save more lives than you think, Chief Shen.” The Commander nods in assent. “How are the Dragon Rounds progressing? Are they ballistic only?”

Good work on the test,” she can almost hear Dad saying, “now, did you finish your homework?

Lily hides a bitter smile. Even the apocalypse won't stop Asian parents.

“We’ve improved on the currently available tracer rounds; those can be deployed. But the Dragon Rounds still explode inside the chamber…”




Despite the massive change in leadership aboard the Avenger, Lily notices the smallest changes first. Sure, there’s a trend towards more survivors after missions, but the soldiers are happier. They really believe they’re going to win this war, even after Central has sent them to hunt down a traitor or a mole. They don’t seem to care that there are thousands of civilians, blissfully ignorant of Dad’s sacrifice to set them free. No, the civilians flock to ADVENT’s hands instead, even as the aliens melt them into green goo.

ROV-R chirps in the specific cadence dedicated to the Command team. Lily sighs. Why do they always bother her when she’s in the middle of something?

“Up late, Chief Shen,” the Commander says as she walks into Engineering, a thermos in hand. “Engineer Andrade is handling the night shift well. What’s keeping you up?”

Lily doesn’t bother pushing up her welder’s mask. “Got work to do.”

“So we all,” the Commander says. “You don’t need me to remind you that rest is important too.”

Lily huffs. “Is there something you need, Commander?”

“On the last mission, we encountered the turrets. You mentioned that they were fully automated.” Lily hears the Commander turn on a tablet. “I’d like to appropriate their systems to defend the Avenger.”

“Our current focus is on the plated armor,” Lily says as she seals the two metal slabs together. “All the engineers are occupied as well.”

“It won’t be long before ADVENT goes after the Avenger directly.” The Commander shifts her stance on the cold metal floors of Engineering. “We need to be prepared. Turrets could provide covering fire, either as the Avenger flies off or personnel escape.”

Lily shuts off the flame. ROV-R swoops down to set the MIG welding gun on its holder. “You think we’ll be shot down.”

“I tried to defend XCOM HQ to my last breath, Chief Shen. We should have evacuated far earlier,” the Commander says. “We were unprepared to deal with hordes of Mutons and Sectopods. This time will be different.”

Unbidden heat builds up in Lily’s ears. You could’ve gotten Dad killed, she thinks, and then I would be an orphan, and all alone in San Francisco. Where would I be then?

“You’ve lost your father,” the other woman continues. “I have no intention of costing you his legacy as well.”

“Why do you care?” Lily hisses.

“I care about my men’s health and safety. Speaking of which, is that gas still on?”

“It’s inert, it’s not the fuel,” Lily snaps, but she closes the valve regardless. “I don’t know what game you’re playing, Commander, but your focus should be on kicking the aliens off the planet, not micromanaging everyone’s feelings.”

“When it interferes with their performance, I need to have a talk.” The Commander taps her fingers against the wall. “We had that scare with your ingestion of god-knows-what sludge. We’ve recorded a second Gauss rifle exploding after overheating. Not up to your usual work. I know you’re working on the problem. I would, however, prefer if you didn’t explode as well.”

“I’m the Chief Engineer, Commander, I know what I’m doing. My team knows when to follow me, and when to work alone. This is just one of the times I want to work alone.”

“Working together is hard.” The Commander scowls. “Particularly when your partners are determined to die of alcohol poisoning.” The older woman’s face softens. Lily thinks she sees a hint of her long dead a boh, a jazz singer who swam from Shenzhen to Hong Kong to escape the communists. “But you may find they offer ideas or companionship far more valuable than their work.”

Is that why you keep Central around? Lily wants to say.

“I like to know my men,” the Commander says. “Understand their strengths, complement their weaknesses, provide camaraderie under fire. It’s what leaders do.” She tilts her head. “Who knows what you’ll learn? It could prove useful.”

"You know, sir, I thought pep talks died with high schools and all that jazz."

The Commander laughs, but there is steel in her voice and ice in her eyes. "I wouldn't patronize you. However, if your work suffers, I will re-evaluate your position on the Avenger."

Lily pauses. Where would she go, if she loses the Avenger? What place in the world would have use for a Taiwanese-American engineer who specializes in robotics? Most Resistance Havens have barely enough wood to get them through the winter, let alone steel and sulfuric acid for circuit boards.

"You know how to change that," the Commander says.

Shen takes a deep breath, trying to find her center. All the stress from twenty years of life on the run and three quarters of a year without her father comes boiling up. Dad said Dr. Vahlen would have some words about that, the biologist that she was. Dr. Vahlen would probably say something about adrenaline and cortisol and all the things Lily memorized once for tests and promptly forgot. Biology is too imprecise. It can only ever be quantified in ones and zeroes. Not like physics, where the significant digits trail off into the thousandths and hundred-thousandths. In physics, things happen at scales so tiny, the mere act of viewing could change their dynamics. Lily likes physics and calculus. They’re quantifiable at one end, and drift into philosophy at the other. Biology and the act of living are a mess all the way through.

Equations won’t help her now. The ground spins beneath her feet. She takes a deep breath. The integral of an exponential function is the exponential function we started with, Lily tells herself, trying to steady herself on firm facts. Newton’s third law of motion – Dad, what was the third law again?

Tears prick at her eyes. Of course Dad isn’t answering. He’s dead, and she watched him waste away.

Strong. Dignified. Unbreakable, even in the face of adversity, a dream her father had encoded in her Chinese name. There’s no use in crying, Lily, her father had told her after looking at the test with a big fat F in the top-right corner. Tears don’t help anything. Be strong. Let’s work on this together. What don’t you understand?

And now, like the girl she was twenty-six years ago, Lily wants to scream at the top of her lungs, “I don’t understand anything!” She presses the heel of her palms to her eyes. Tears are building up at the bridge of her nose. She breathes in. There’s fluid clogging her sinuses and pressure building in her chest. This equilibrium cannot hold.

“You know where to find me,” the Commander continues, turning to leave, “when you are ready.”

I’m not ready!” Lily screams, and it all comes bursting out. “Dad is the only parent I’ve ever had, and he’s gone!"

The Commander leaves the room, and Lily collapses against the bench to sob her heart out.


Lily hardly notices the clink of a mug against the workbench. She can barely smell the musty odor of mushroom tea, XCOM’s sad substitute for actual tea. She does notice the handkerchief brushing against her fingers. She grabs the fabric and furiously wipes her eyes until she sees pink.

“I’m twenty years older than you. I still miss my mama he baba." The Mandarin words are soft and shushing, tinged with Southern Chinese tones. Dad would know where the Commander's accent came from. "It doesn’t go away. The pain just… dulls, until it’s manageable.”

“How’s that supposed to make me feel better?” Lily chokes out.

“It’s not. We persist,” the Commander says, “despite what life throws at us. And we make the ones we love proud.”

“I want Dad here,” Lily whispers, “I want him to see all that I’ve done.”

“So do I,” the Commander says, and gives Lily another dry handkerchief. “But until we see them again, we’ll have to make do. Why don’t you have a drink? That is fluid you’re losing, after all.”

"I really hate it when you do that," Lily says, but drinks regardless. "I'm not a project that needs to be fixed."

The Commander sighs, and looks around. The Engineering Bay is clear; Andrade must have gone to staff the Power Relay.

"Can you keep a secret?" she asks.

"ROV-R's not a chatty one."

"I have no idea what I'm doing," the Commander confesses. "I'm used to having hundreds of men and organizations at my disposal. But I recognize some things that I can do. And I try to make up for the things I can't by relying on those who can."

"So that's why you're going around, playing counselor?"

"That, and I also care about those under my command." She levels a meaningful glance at Lily. "Particularly when things start exploding without the men improvising."

Lily laughs a bit, and sips from the mug. "Got it, sir. I'll try to keep the explosions to a minimum."

"Glad to hear it. We'll talk soon." The Commander straightens. "Goodnight to you too, ROV-R."

The Chief Engineer starts to wonder if Dad was going soft in his old age.

She returns to work, the invisible burden on her shoulders imperceptibly lifted.