At 7:12 a.m. in Denver, Colorado, my ninety-pound German Shepherd threw her whole body against my bedroom door like someone was trying to kill me on the other side.

Her claws skidded on the hardwood. The frame shook. A picture on the hallway wall rattled so hard it tilted sideways. Her teeth were bared, eyes wild, a deep growl vibrating out of her chest like distant thunder rolling over the Rockies.

Two hours later, twenty-three of my coworkers were dead in a glass office building off I-25, in a conference room I was supposed to be sitting in.

My name is Marcus Rivera. I’m thirty-two, a software engineer, and until that day I worked for a tech startup in Denver’s Tech Center. The thing that saved my life wasn’t a seatbelt or a doctor or dumb luck.

It was my dog.
And the person who died in my place was my little sister.

For seven years, Luna had never growled at me. Not once. Not when I accidentally stepped on her tail at our old place in Aurora. Not when I forgot her dinner after pulling an all-nighter on a release. Not even during Colorado’s summer thunderstorms when the sky turned green and the thunder shook the windows and she tried to crawl under my bed like a forty-kilo puppy.

She was the calm one. I was the anxious mess.

Every weekday for the last four years of my life followed the same script. Alarm at 5:30 a.m. Luna would already be sitting beside the bed, ears perked, tail thumping against the nightstand just hard enough to rattle my phone. Coffee for me, breakfast for her. Quick loop around our quiet neighborhood in southeast Denver the one with the maple trees and the same old guy jogging in a Broncos hoodie no matter the season then I’d shower, dress, and drive twenty minutes down to our office off Orchard Road.

Luna thrived on routine. Honestly, I did too. It made me feel like my life was finally something other than chaos.

That Tuesday in March was supposed to be the biggest day of my career. Our startup was finally launching the app we’d been building for two years. Investors were flying in. Our CEO, Derek, had been pacing holes into the carpet for weeks talking about “life-changing equity events” and “generational wealth.”

We all laughed when he said it, but a part of me believed him. For once, it felt like maybe I hadn’t screwed everything up.

My sister Sophia had gotten me the job in the first place. I’d been unemployed, living on instant ramen and panic after getting laid off from a bigger company. Sophia called one night from her office in downtown Denver.

“Send me your resume,” she ordered. “We need a backend engineer, and Derek trusts my judgment. Don’t make me regret this.”

She was twenty-eight then, two years younger than me, but she’d always been the responsible one. The kid who color-coded her middle school binders. The first in our family to buy a house, a tiny two-bedroom in Lakewood with yellow siding and a yard she actually kept mowed. She’d organized our dad’s medical bills when he had his heart attack. She handled our mom’s move into a smaller apartment when the rent in our old neighborhood got too high.

She kept everything together while I…showed up late with takeout and apologies.

The Monday night before the launch, she texted me while I was debugging a stubborn memory leak.

Don’t forget tomorrow. 8:00 a.m. sharp. Conference Room A. Equity packages. Derek is finally announcing numbers.

I stared at the message for a long time. Equity packages. Money that wasn’t “scraping by,” but “maybe pay off Mom’s car” money. “Maybe fix Dad’s roof” money.

I’ll be there, I typed back. Want me to pick you up?

Nope, I need to get there early to set up. But don’t you dare be late, Mark. I’ve been talking you up to Derek for months.

That was Sophia. Always two steps ahead, always putting my name in rooms I hadn’t earned yet.

The first thing that went wrong that morning was the time I woke up.

It wasn’t my alarm that dragged me out of sleep at 4:03 a.m. It was Luna’s paw on my shoulder.

She wasn’t gentle about it either. Not the tentative tap she used when she needed to go outside. This was hard, almost frantic. Tap-tap-tap.

“Okay, okay, I’m up,” I muttered, still half asleep.

She whined. Not her “I’m hungry” whine. Not her “squirrel in the yard” whine. This sound was raw, almost panicked. Her breath came fast and shallow. I could feel her muscles trembling under my hand.

“What’s wrong, girl?” I sat up, heart speed-running, and she instantly jumped off the bed and trotted to the bedroom door. She looked back once to make sure I was watching, then scratched at the door with a sharp, urgent claw.

I stumbled after her, sleep-blurry, scanning the dark apartment. One bedroom, half-unpacked boxes in the corner, cheap IKEA bookshelf, small living room, balcony overlooking the parking lot. Nothing out of place. No broken window. No stranger lurking in the hallway.

I cracked open the front door to the hallway of my third-floor walk-up. Empty. The same ugly brown carpet. The same flickering exit sign. But the air smelled…off.

Something metallic and sweet tickled the back of my throat. Not strong. Just enough that I noticed.

“Probably someone spilled something,” I muttered to myself. Denver apartment buildings always smelled like some combination of old carpet, cooking oil, and other people’s laundry detergent.

I opened the sliding door to the balcony to let Luna out in case she needed to throw up or something. She took one look at the outside air, then backed up fast, whining like I’d suggested we jump off the railing.

“Seriously?” I whispered. “What is going on with you?”

She ignored the open door and latched her teeth onto the hem of my pajama pants, tugging me back toward the bedroom. I’d seen her herd kids away from the edge of a pool before, but never me.

I checked her paws, her ears, her eyes. Her nose was cold, her gums pink, no limp, no visible injury. Physically, she seemed fine. But her whole body was wired tight, every muscle drawn like a bowstring.

“Okay, so we’re just…weird today,” I said, trying to laugh it off. “You’re allowed to have a weird day.”

I tried to lie back down. Luna did something she knew she wasn’t supposed to do.

She jumped on the bed.

This dog had respected the “no dogs on furniture” rule since the week I brought her home from a rescue in Aurora. I’d eaten entire pizzas on the couch while she sat on the floor ignoring the pepperoni. She was that dog.

Now she climbed onto my chest, all muscle and weight, and planted herself between me and the door. Every time I shifted like I was about to get up, she leaned her weight into me and let out a low rumble.

By 5:30 a.m., my alarm started blaring, its usual obnoxious tone. Luna flinched at the sound but didn’t move.

“Big day, girl,” I told her, reaching for my phone. “Derek said ‘life-changing’ like fifteen times yesterday. Sophia would murder me if I blew this.”

At the mention of Sophia, Luna’s ears twitched. She knew that name. My sister was her favorite human second only to me. Sophia always brought treats, always scratched that one spot behind Luna’s collar that made her kick her back leg.

I swung my legs off the bed.

Luna reacted like I’d pulled a fire alarm. She hopped off the mattress and beat me to the doorway, planting herself directly in front of it. Her stance widened, head lowered, eyes locked on me.

“Move,” I said, pointing. She’d never disobeyed that command before.

She didn’t even blink.

I stepped to the left. She mirrored me. I stepped to the right. So did she. Under any other circumstances, it would’ve looked like we were dancing. In that moment, it felt like my dog was silently telling me, over my dead body.

“Luna,” I said more firmly. “I have to go to work.”

That’s when she growled.

It started deep, deep in her chest, a sound I’d only heard once before when an aggressive off-leash dog had charged at us at Washington Park. Her lips lifted, showing white teeth I’d never seen directed at me. Her fur stood up in a dark ridge along her back.

I froze.

“This isn’t funny,” I said, my voice coming out thinner than I wanted.

She took one step closer, positioning herself so that her body physically blocked the doorknob.

My phone vibrated on the nightstand, screen lighting up with a picture of Sophia in a stupid elf hat from last Christmas, grinning at the camera while Luna tried to lick frosting off her cheek.

“Please tell me you’re in your car,” Sophia said the second I answered. No hello, no good morning.

“I’m…not,” I admitted. “Something’s wrong with Luna. She won’t let me leave my room. She’s freaking out.”

“You did not just hit me with ‘my dog ate my homework’ on equity day,” she snapped. “Marcus.”

“I’m serious. She’s growling at me.”

“Then put her in the bathroom, shut the door, and go. Derek specifically asked if you’d be there. This isn’t just about you. This is about both of us.”

I could hear the edge in her voice, the disappointment. She had stuck her neck out for me over and over again at that office. She’d smoothed things over when my social anxiety made me freeze in stand-ups. She’d rewritten my emails when they sounded too abrupt. Every success I had there had her fingerprints on it.

“Give me ten minutes,” I said. “I’ll figure something out.”

“You have five,” she said and hung up.

I stared at the dark screen for a second, then slid my phone into my pocket. When I looked up, Luna was staring at me like her entire world depended on what I did next.

She watched me walk to the closet. Watched me pull on my jeans, button my shirt, tie my shoes. Every time my hand moved toward my laptop bag, her growl returned, low and pleading.

“Hey,” I said softly, crouching down so we were eye level. “What are you so scared of, huh?”

She flicked her gaze from my face to the door, back to my face. Her tail was tucked. Her ears were pinned flat. If she could speak English, I knew she’d be saying one word: no.

A car engine rattled outside, the familiar, embarrassing cough of Sophia’s ancient Honda. She could afford something nicer now, but she refused to replace the car she’d driven since college.

“Still runs,” she’d always say. “Why waste money?”

Luna heard it too. The moment Sophia’s footsteps hit the stairs outside my apartment, Luna detonated.

She threw herself at the bedroom door like something on the other side was trying to break in. Barking, growling, scratching. Deliberate, wild. Wood splinters started shaving off with each claw strike.

“Soph’s going to think I’ve lost it,” I muttered.

Her knock came a second later. Solid, annoyed.

“Marcus, open this door. We’re going to be late.”

Luna’s growls morphed into a sound I’d never heard from her before, something between a howl and a scream. She rammed her shoulder into the door so hard the hinges protested.

I grabbed for her collar, terrified she was going to hurt herself. She spun on me, teeth flashing, stopping her mouth an inch away from my hand. She didn’t bite. She didn’t snap. She just held there, trembling, eyes blown wide with terror. Not of me.

Of whatever was out there.

“That’s it, I’m using my key,” Sophia’s voice came through the door, sharp and offended now. I’d given her a spare for emergencies.

I heard the jingle of keys. Luna heard it too. She launched herself upward, paws slamming into the deadbolt, and by some miracle of timing, her weight hit the lock just as Sophia tried to turn the key from the other side, flicking it firmly into the locked position.

“Did you just lock me out?” Sophia demanded. “Are you serious right now?”

My phone lit up again. Incoming call: SOPHIA.

I answered, heart pounding, Luna still wedged against the door.

“What the hell, Mark?” she exploded. “You lock me out of your place now? Over what, some weird dog mood?”

“I swear to you, something’s wrong,” I said. “She has never acted like this. Ever. She’s not herself.”

There was a pause on the other end, a small crack of hesitation.

“Your dog is not an omen,” she said finally, her tone tired. “She’s…a dog. You’re scared. I get it. This is a big day. But you cannot hide in your apartment and blame your dog. Not again.”

She wasn’t wrong about my track record. When Dad had his heart attack three years ago, I’d stood frozen in the hospital parking lot, unable to walk inside. I’d texted Sophia some excuse about traffic while she handled the doctors, the paperwork, Mom’s tears.

When our grandmother died, I’d missed the funeral entirely, claiming a “critical deploy” that everyone including Sophia knew was a lie. She’d covered for me with the family anyway.

I deserved her anger. Just not today. Not for this.

“Look through your peephole,” she said, voice softening. “It’s just me. Do I look dangerous?”

I hesitated, then stood up. Luna’s head tracked me like a surveillance camera. When she realized I was moving toward the bedroom door, she planted herself in front of it again but this time, instead of growling, she whined. A high, desperate sound.

I pressed my eye to the peephole in the front door. There she was: Sophia in her navy blazer, her hair pulled back in the same no-nonsense ponytail she’d worn since high school. Phone in one hand. Keys in the other. Brow furrowed, jaw set.

She saw the peephole darken and lifted her hand in a little wave, forcing a smile.

“It’s me,” her voice filtered through the wood. “Your annoying little sister. Open the door, idiot.”

Luna body-checked the bedroom door so hard it shook. She came back to me, planted her paws on my chest, and pushed. Not playfully. Deliberately, like she was physically trying to move me away from the front of the apartment.

She sat, pressed her paws against me, and looked right into my eyes. No growl. No bark. Just a soft, miserable whine.

“Fine,” Sophia said on the other side, frustration boiling over. “You know what? Do whatever you want. I have to go. When Derek fires you, don’t call me. When you can’t pay rent, don’t call me. I’m done being your safety net, Marcus.”

Her footsteps stormed down the stairs. The car door slammed. The engine rattled back to life and faded down the street.

The entire apartment fell quiet. The only sound was Luna’s breathing, still too fast. She slumped against my legs, suddenly boneless, like every muscle that had been holding her in that rigid stance finally let go.

I sank onto the edge of the bed, guilt crashing over me in a hot wave.

“What did I just do?” I whispered.

On one side of the scale: the biggest opportunity of my career, my sister’s trust, my boss’s expectations. On the other: my dog’s panic and a faint, metallic smell in a Denver apartment building.

I’d chosen the dog.

I waited for regret to kick in like it always did when I bailed. It didn’t. There was only a pounding in my chest and a low, electrical hum under my skin.

I called Derek’s direct line. The man answered calls in the middle of elevator rides, during workouts, even once during his own wedding ceremony according to office legend. This morning, his phone rang, and rang, and went to voicemail.

“Hey, Derek, it’s Marcus,” I said, heart hammering. “I’m having…a medical emergency.” I scrambled for words. “I can’t make it into the office, but I can dial in. I’ll have my part of the presentation ready to screen-share. I’m really sorry about the timing.”

Medical emergency was technically true. I was having some kind of psychological meltdown in my bedroom while my dog guarded the door like a soldier.

I opened my laptop on the little desk pressed against the window. Luna followed, flopping down at my feet, still keeping one wary eye on the hallway.

I logged into Slack, expecting the usual wall of messages. Jokes, random memes in #random, Sophia’s “Let’s do this!” pep talk in #general.

The last message in #general was from Sophia at 7:45 a.m.

Conference Room A is ready. Coffee, pastries, equity dreams. See everyone at 8:00. Let’s change our lives.

No little emoji reactions. No follow-ups. No “running late” comments.

I checked our project channel. Quiet. I clicked over to Instagram. Our designer Rachel usually posted at least three stories before 9:00: latte art, office selfies, her walk to the light rail. Nothing.

My stomach did something unpleasant.

“Maybe they’re all actually working for once,” I muttered, but even I didn’t believe it.

Luna lifted her head and sniffed the air again, nose twitching, ears alert. The faint metallic sweetness was stronger now. Not overwhelming, but wrong. If you’ve ever walked into a room and immediately known something was off without being able to say what, that was it.

As a senior engineer, I had admin access to an internal tool for debugging our office door sensors and badge readers. It included live feeds from a few security cameras. I’d only used it once to fix a bug in our door logs.

Now my fingers moved on autopilot. VPN on. Two-factor code. Internal URL. Camera dashboard.

First feed: parking lot. There was Sophia’s Honda in her usual spot near the front entrance of our building off East Belleview. Derek’s gleaming white Tesla was pulled into the CEO spot, charger cable dangling. The lot was full. Everybody was there.

Second feed: lobby. Our receptionist Jake’s desk sat in the middle, the little bowl of candy he kept refilled every week visible near the edge. His chair was turned slightly toward the hallway.

But he wasn’t on the phone, didn’t have his head bent over his keyboard, didn’t spin in his chair like he usually did when he was bored.

He just…sat there. Too still. Back a little too straight. Something about the posture made my scalp prickle.

I clicked to another camera: kitchen area. Empty.

Ping-pong room. Empty.

Open office floor. I recognized the rows of desks, the potted ficus that drooped no matter how much water it got, the motivational poster Derek had ordered off some startup website. The chairs were occupied.

Everyone was sitting, just like on a normal morning. But no one was moving. No one was leaning back in their chairs. No one was gesturing, or standing, or spinning idly like Tommy always did.

It was like someone had pressed pause on a full floor of people.

“Okay, that’s weird,” I whispered. “That’s ”

My phone exploded in my hand, vibrating nonstop as call after call came in from the same number: Derek.

He called five times in rapid succession. On the sixth, I finally swiped to answer.

“Hello?”

“Marcus.” His voice didn’t sound like Derek. The brisk, self-assured CEO I knew was gone. In his place was someone gasping for air between words. “Don’t come here. Do you hear me? Do not come to the office.”

There were sirens screaming in the background. Voices shouting. A muffled announcement from what sounded like a fire truck or an ambulance. My heart slammed into my ribs.

“What’s happening?” I asked, already knowing I wasn’t going to like the answer. “Where’s Sophia? Is she okay?”

He made a sound I’d never heard from another adult man. Half sob, half attempt at speech.

“They’re all dead,” he choked. “Everyone in that room. Twenty-three people. Oh God.”

The apartment spun. I grabbed the edge of the desk to steady myself.

“That’s not funny,” I said, my voice barely a whisper. “What do you mean dead? From what? How?”

Derek sucked in a ragged breath. I could hear someone on his end telling him to sit down, to slow his breathing.

“I was late,” he said. “My Tesla wouldn’t start. The stupid software update. It locked the car until it finished.” He gave a hysterical little laugh that died instantly. “I thought I was going to miss my own meeting.”

He inhaled again, shaky.

“When I got here around nine-thirty, the parking lot was full. But when I walked inside, the lobby was quiet. Jake was at his desk, but he wasn’t answering me. I went over to yell at him for ignoring me and…he didn’t move. He was just sitting there.”

My eyes flicked to the camera feed again. Jake, frozen at his desk.

“His eyes were open,” Derek continued, his voice cracking. “But they weren’t…they didn’t look right. They were pale. And his skin was kind of…bluish.”

He didn’t go into detail. He didn’t have to. My imagination filled in enough to make me swallow hard. No blood. No violence. Just the wrong kind of stillness.

“I ran to Conference Room A,” he said. “I thought maybe it was some horrible prank, I don’t know. But they were all there, Marcus. Sitting in their chairs like the meeting was still happening. Sophia, Tommy, Rachel…everyone. Heads slumped, some of them tipped back. Their eyes ” His voice broke. “They looked like they fell asleep and never woke up.”

I slid down the wall until I was on the floor. Luna pressed herself against my side, whining low, like she could hear every word.

“The building manager says it was carbon monoxide,” Derek said.

I closed my eyes.

Carbon monoxide. The invisible, odorless gas they warn you about in elementary school safety videos. The one you’re supposed to have detectors for. The one that kills families in their sleep.

“The new heating system,” Derek went on. “The one we rushed to install last week so the office wouldn’t freeze during the investor visit? They installed a valve backward. The exhaust didn’t vent outside. It fed straight into the ventilation system.”

My mind flashed back to the faint metallic sweetness in my hallway, Luna refusing to go out, panicking at the front door.

“We didn’t have carbon monoxide detectors in the conference room,” Derek said. “The building’s old. It met the code when it was built twenty years ago. Nobody thought ”

He cut himself off with a choked sob.

“The system kicked on around seven-forty-five. Closed room. No open windows. They probably just felt drowsy. Like they’d pulled an all-nighter. By the time they realized something was wrong, they couldn’t stand up.”

My brain struggled to hold the information. Twenty-three people. Less than an hour. A sealed conference room becoming a box of poisoned air.

“Where’s Sophia?” I asked again, because he hadn’t answered that part and my body refused to accept what it already knew.

He went quiet. So quiet I thought the call had dropped.

“Derek,” I said. “Where is my sister?”

“She wasn’t in the conference room,” he said finally, his voice small. “She was at your desk.”

I couldn’t process the words.

“What do you mean?” My voice sounded strangled. “Why would she be at my desk? She was supposed to be in that meeting.”

“The security footage shows her leaving Conference Room A at 8:10,” Derek said. “About five minutes after the meeting started. She took your laptop with her. She went to your station. She was…trying to log you into the meeting remotely. To make it look like you were there.”

The air left my lungs in a rush. I saw it in my mind as clearly as if I’d watched the footage: Sophia standing up from the conference table, rolling her eyes at whatever excuse she was about to make for me. Carrying my laptop down the hall. Sitting in my chair. Typing my password.

“She knew your login,” Derek said. “She was always covering for you. She opened the conference link, set it to use your camera. If anyone in that room had still been conscious enough to look at the big screen, they would have seen her at your desk instead of you.”

My sister had gotten up from the table of twenty-three people and walked straight into a different pocket of poisoned air. She’d died alone at my station, trying to protect me from the consequences of another one of my screw-ups.

“The paramedics found her slumped over your keyboard,” Derek said quietly. “Your computer was still on.”

I didn’t remember hanging up. One second Derek’s voice was in my ear, the next I was staring at my phone on the floor, screen gone dark. My own reflection looked back at me, ghost-pale, eyes wide.

My ears rang. My chest hurt. Luna nudged my hand with her nose, forcing my fingers open. I grabbed her collar and buried my face in her fur.

Sophia’s last words before she stormed off echoed in my head. I’m done being your safety net.

She hadn’t been. Even furious, even when she thought I was hiding behind my dog, she had gotten up from that table to shield me one last time.

Two months later, I stood in Fort Logan National Cemetery outside Denver, the March wind cutting through my black suit, holding a bunch of sunflowers Sophia’s favorite while Luna sat pressed against my leg.

The stone with her name was still too new, the letters too sharp.

SOPHIA RIVERA
BELOVED DAUGHTER, SISTER, FRIEND
1994–2023

Someone that practical shouldn’t have loved something as bright and ridiculous as sunflowers. But that was Sophia. Spreadsheets and sunshine.

We’d been back to this spot a lot in the weeks since the mass casualty incident in the Denver Tech Center made national news. There were investigations, statements from the fire department about outdated building codes, somber press conferences on local stations, a short segment on national morning shows about “the silent killer in our offices.”

There were lawsuits. So many lawsuits.

The contractor who’d installed the heating system had rushed the job. The city inspector had missed obvious mistakes. The building was old enough that carbon monoxide detectors weren’t required in every room. There was a settlement fund for the families of the twenty-three victims.

The check that came in the mail with my name on it made me want to set it on fire. Money with the weight of my sister’s life baked into it. Money because she’d died in my chair.

I tried to refuse it. My parents, hollow-eyed with grief, insisted.

“Don’t you dare waste her sacrifice,” my mother said, voice hoarse. “Do something with it. Something she would be proud of.”

So I did.

The Sophia Rivera Foundation started two weeks after I signed my name on deposit slips with shaking hands. Its mission statement was simple: free or low-cost carbon monoxide detectors and air quality monitoring for small businesses and nonprofits across Colorado that couldn’t afford top-tier safety systems. Offices like ours. Buildings like ours.

In eight weeks, we’d installed monitors in forty-seven offices, clinics, and kitchens across Denver, Aurora, and Lakewood. In three of them, the technicians found existing leaks serious enough that they had to shut things down immediately.

Three near disasters. Seventeen kids at a daycare sent home early because levels were rising instead of being tucked in for naptime under a ceiling full of poison. A family restaurant on Colfax that closed one Friday night instead of serving food in slowly toxic air. A dental clinic where a faulty furnace got replaced before patients ever smelled something strange.

Luna came with me to every installation. At first, I just couldn’t stand to leave her alone for long stretches. She was my lifeline when the nightmares got bad. But one of the safety consultants noticed how intently she sniffed vents, how she avoided one particular mechanical room long before sensors chimed.

“You know German Shepherds are used for detection work, right?” the guy said, scratching her behind the ear. “Drugs, explosives, bed bugs, all kinds of stuff. Their noses are insane.”

We started training with a local canine detection trainer. Not for carbon monoxide itself that gas has no odor but for certain other compounds and changes that often accompany malfunctions and leaks: exhaust, fumes, burning insulation. She already had the instinct. We just put structure around it.

Within a month, she’d alerted reliably in three different buildings to problems the human inspectors confirmed later.

She’d always been my pet. Now she was my partner.

The hardest thing I had to do wasn’t talking to lawyers, or sitting through depositions, or explaining the same nightmare morning to investigators over and over until the words lost meaning. It was reading the letter Sophia left behind.

The fire department returned her small box of personal items from the office: her badge, her favorite pen, a chipped coffee mug that said “World’s Okayest Office Manager,” and an unsealed envelope with my name on it, dated one week before she died.

I didn’t open it right away. It sat on my kitchen table for days, accusing me silently every time I walked past. One night, when the apartment felt too quiet and the wind rattled the windows just the way it had the night she drove away, I finally slid my finger under the flap.

Her handwriting slanted across the page, familiar and painful.

Mark,

I’m writing this because I’m too mad to say it to your face, and if I wait until I’m not mad, I’ll never say it.

You missed Dad’s birthday dinner again. Mom cried. I made excuses for you (again), because that’s what I do. That’s what BIG sisters are supposed to do, except I’m younger than you and somehow still more responsible. It’s ridiculous.

Here’s the thing: I will probably always cover for you. Because I love you. Because you’re brilliant and soft and you panic over stuff other people find easy. But I am begging you at some point, you have to stop letting fear drive the car.

You hide behind “I’m anxious” a lot. Sometimes that’s real. Sometimes it’s an excuse. You’re smarter than everyone in that office and you act like you’re going to be found out as a fraud any minute. Newsflash: they need you. Stop hiding.

And please, for the love of God, trust Luna. That dog knows you better than you know yourself. She’d literally die for you. Make sure you are living a life that deserves that kind of loyalty.

Also, I updated my life insurance. You’re the beneficiary now. Don’t argue with me about it. If something happens to me (don’t freak out, I’m not planning to get hit by a bus), use it to help people. That’s not a suggestion. That’s an order.

Love,
Your annoying little sister
(aka your permanent safety net, whether you like it or not)

P.S. If you forget Mom’s birthday again, I will haunt you.

I sat there at my kitchen table in Denver, letter trembling in my hands, while Luna rested her head in my lap. Sophia had known exactly who I was, all my flaws and fears, and she’d loved me anyway. She’d planned for a future she wouldn’t live to see.

The foundation. The free detectors. The training classes packed with business owners who’d never thought about carbon monoxide in their old buildings. All of it felt less like a noble decision and more like following instructions I’d been given before the world ended.

Now, standing by her grave beneath an enormous Colorado sky, I knelt down to lay the sunflowers along the base of the stone. Luna lowered her head until it almost touched the cold granite.

“We found another leak last week,” I told her, my voice low. “Daycare center in Aurora. Seventeen kids. Three teachers. The furnace was cracked. Levels were already climbing when we got there.”

The wind tugged at my coat. In the distance, someone else’s funeral service murmured.

“Luna refused to go past the hallway,” I said. “She kept pawing at the vent. The inspector checked because of her. They evacuated everyone. Nobody got sick. Everybody went home.”

My throat tightened. I pressed my palm against the stone, tracing the R in Rivera.

“I’m trying to make it count, Soph,” I whispered. “Your life. The money. The guilt. All of it. I can’t fix what happened in that conference room. But I can make sure fewer people die because someone thought detectors were optional.”

Luna let out one sharp bark. It echoed across the rows of white stones, then faded into the open air. It sounded, impossibly, like agreement.

We had three more installations scheduled that afternoon. A pediatric clinic in Englewood. A family-owned Mexican restaurant on Federal Boulevard. A dog grooming salon in a converted bungalow, the kind of place where every inch smelled like shampoo and wet fur.

On the drive out of the cemetery, my phone buzzed with a text from an unknown number attached to a local Denver news station.

Hi Marcus, this is Allison from Channel 7. We’d love to do a follow-up piece on the foundation and how Luna is helping save lives. Human-interest angle. Are you available next week?

Sophia would’ve hated the attention. She’d worked behind keyboards and clipboards, not in front of cameras.

I typed back: Thanks, but we’re going to keep things low-key. Happy to share resources on CO safety though.

I hit send and tossed the phone onto the passenger seat.

Luna shifted into the space where my sister used to sit on our rare shared commutes. She stuck her head out the window as we merged onto I-25, ears flapping in the dry Colorado wind, tongue lolling in a goofy dog smile that somehow existed in the same universe as all that grief.

People like to say “everything happens for a reason.” They said it at the memorial service for my coworkers. At church. In hushed voices at King Soopers when they recognized me from the news. They meant well.

They were wrong.

There is no good reason for twenty-three people to die in their office chairs on a Tuesday morning in Denver. No lesson big enough. No cosmic ledger balanced.

But meaning is different. Meaning is something you build yourself out of the broken pieces.

Maybe the reason doesn’t exist. Maybe it doesn’t matter. What matters is this: a German Shepherd in Colorado refused to let her human leave an apartment one morning. A younger sister walked into a poisoned building with a laptop under her arm because she still believed he could be better. A man who’d been afraid of everything his whole life finally decided to trust his instincts and his dog.

Now, every time Luna stiffens in front of a vent, every time a sensor beeps in a warehouse in Aurora or a bakery in Boulder or a salon in downtown Denver, I think of Sophia. I imagine her rolling her eyes at my clumsy speeches, at the way my voice still shakes when I talk about her.

“Look at you,” I can hear her saying. “Saving people. Actually showing up.”

Luna nudged my arm with her nose, demanding a scratch behind the ears. I obliged, keeping one hand on the steering wheel as the Denver skyline grew smaller in the rearview mirror and the road opened up ahead.

I’m not the hero of this story. I’m the idiot who almost ignored his dog. The coward who let his sister die trying to cover for him. But I get to wake up every morning. I get to drink my coffee, clip Luna’s leash, and walk out the door she once spent an hour trying to keep me from opening.

So if you ever see your pet act strange staring at a corner of the room, refusing to go inside somewhere, blocking your way with that stubborn animal body don’t laugh it off right away. Don’t assume it’s nothing.

Sometimes, in a third-floor apartment in Denver or a quiet house in any city in the United States, the only alarm that goes off in time isn’t the one you bought at Home Depot.

It’s the one with fur and four paws who decided that, today, you’re not going anywhere.