The basement lab is where my father worked after leaving Cartaxus. I spent countless evenings down here, working with him, helping him label samples and calibrate the machines. There isn’t a single device down here I couldn’t take apart and reassemble unassisted, and in the vast library of my father’s famous code, a handful of the algorithms are mine. I tug a string beside the door, and the ancient fluorescent bars on the ceiling blink lazily to life. A weight slides from my shoulders as I scan the overflowing filing cabinets, the counter cluttered with notes, and the hulking gray machines bolted to the walls. Everything is just as I left it.

“This is a disaster zone,” Cole mutters. “Any weapons in here, Catarina?”

Six at last count, but I roll my eyes. “This is a place of science.”

He snorts. “How about you talk me through what you’re going to do.”

“I’ll need a scalpel,” I say, knowing this is the part he’ll object to most, after my last attempt to kill him. I point to a lacquered-oak cabinet in the corner of the room, its doors plastered with stickers and charts. “They’re kept in there, plastic-wrapped and sterilized. I have about four left.”

“Okay.”

“And I’ll need my genkit. It’s in a drawer under the counter.”

“That’s fine. What will you be doing?”

“I need a dose from the freezer,” I say, “then I’ll cut it open to get a fresh sample to sequence, and detonate the rest in a pressure box to measure the blast. That’s all.”

He nods, scanning the room. “Wait here, then. I’ll go and get your sample.”

He jogs upstairs to the freezer. My eyes stray to the cabinet in the corner. The four scalpels he knows about, but I didn’t mention the gun taped to the second shelf, or the little brown pills stapled to the bottom – pills I made in this very lab, synthesized from the root of a flower people used to sing about in old-world lullabies. A flower I hunted to the far corners of our property to find.

I count the steps between me and the cabinet, eye the rusted hinges on the door. I won’t get to the gun, not enough time, but the pills I can probably handle. With them, I’ll at least have a chance of getting away if Cole turns on me.

I hesitate, glancing at the ceiling, where Cole’s weight is moving swiftly across the floor upstairs.

“Just one slice?” he shouts down, his voice muffled through the walls. His footsteps creak above me, followed by the whine of the freezer’s hinges.

“Yeah,” I shout back, darting silently to the cabinet. “Get a big one if you can.”

“Okay, got one,” he shouts back.

I drop instantly to my knees beside the cabinet, reaching underneath to the plastic pouch I stapled to the wood. Six tiny pills no bigger than a matchstick head, rough balls of resin that look like rancid candy but pack a punch far deadlier than anything else in the house. I yank the packet free and run back to the chair, shoving the pills into my bra just as Cole’s footsteps sound on the stairs.

“Okay, one chunk of frozen dead guy coming up,” he says, swinging open the door. I give him a quick half-smile, a sheen of sweat forming on my forehead.

He pauses in the doorway, scanning my face, my hands. A crease forms between his brows.

I hold my empty hands up, waving them to him. “We can defrost it in the microwave,” I say, jerking my head towards the counter. “Don’t go over a minute though, or it’ll blow.”

He shifts his gaze to my eyes, staring with a fierceness that starts a vein pulsing in my eyelid.

“You didn’t mention the microwave,” he says finally.

I blow out a breath. He thinks I’ve laid a trap. “Sorry, I forgot. You can just put it on the counter and wait for it to thaw, it shouldn’t take long.”

He looks over me slowly, pausing on my chest where one edge of the plastic pouch is digging into my skin, every nerve aflame with tension. I resist the urge to look down, to give away the pills with a single glance.

“Are you trying to kill me again, Catarina?” he asks gently.

“No, I promise,” I say, realizing that it’s easier to meet someone’s eyes than avoid them when you’re lying.

Cole watches me a moment longer, then steps into the room. “You said a minute in the microwave for the sample?”

I let out a breath. “Better make it forty seconds.”

I slide my genkit from the drawer as Cole punches numbers into the microwave. The genkit’s screen is cracked in one corner, the hard drive ancient and prone to overheating, but it runs on a hacked solar battery and still works after two years of constant abuse.

“Come on,” I mutter, holding down the power switch. I have a new one upstairs with a biochip and holoscreen, but it wouldn’t let me log in without software updates from a company that went down with everything else in the plague. The tinny speakers chime as seventy-percent of the screen flickers to life.

“Okay, scalpel time,” I say, swinging open the cabinet. The microwave pings, but Cole’s eyes never leave my hands as I pull out one plastic-wrapped blade and set it on the counter with a petri dish. Cole tips the slice from its plastic pouch, sliding it with a splat into the dish, then steps back, putting a few feet of distance between me and the scalpel.

“First, a sample to sequence,” I say. “Have to get a fresh cut where the cells are less degraded.”

I cut into the slice lengthwise, the meat falling open to reveal the dark stippling of muscle fibers, a dozen tiny drops of blood swelling from severed capillaries. I run a swab along the fresh incision, a crimson blush smearing the cotton, and shake it in a canister of purified water until the liquid blooms pink.

“This should only take a few minutes to sample,” I say. “But stripping Hydra’s DNA from the man’s might take up to an hour.” I snap the canister into my father’s sequencer, its complex internal mechanisms protected by a cast-iron shell that lends it the look of an old-fashioned gas tank. “And the rest,” I say, picking up the butterflied meat, “goes here.”

I pop the lid of a glass box reinforced with steel seams inlaid across each panel. The inside surfaces are rough, lined with countless microscopic scratches that lend it a worn, antique look. Below the box a screen flashes green, square numbers ticking up and down, settling finally on seventy-eight grams.

“And now we wait.” I settle back into the chair, my foot tapping a nervous staccato on the tiles. The wall above the box is marked with two axes, above which twenty-seven dots form a noisy upwards arc. The measurements are multicolored, handwritten dates variously careless and neat, giving the chart the look of a doorway on which children’s heights are scribbled as they grow.

Through the dots, I’ve traced three potential trend lines: one linear, one quadratic, and the third a terrifying exponential. Today’s measurement, three months out from the others, should narrow the possibilities down to one.

“What will this tell us?” Cole asks.

“The estimated blast radius,” I say, pointing to the chart. “It’s been growing, but the pattern’s noisy. Hydra’s evolving, just like any other virus, and the thing that ensures its survival is how far the blasts spread.” I wave one hand across the scattered dots on the wall. “Evolution is the survival of the fittest, and for Hydra that means -“

“That means as the human population scatters, the explosions are getting stronger.” Cole straightens, his eyes leaving me, leaving the glittering scalpel within my reach, and stares wide-eyed at the chart. “Lachlan didn’t mention this. We haven’t been tracking this at the base.” He steps to the glass box. “Why did he leave this apparatus here?”

“Because it’s not his.”

“But this research…”

“It’s not his research,” I say. “It’s mine. I guessed the radius would grow, so I built that box and made the chart. I went into town every month for samples until my bike broke last winter.”

Cole blinks, opens his mouth and then closes it. “Well, aren’t you something,” he breathes.

I shift, awkward under his gaze, something trembling inside me. Then a crack tears through the air as the box blows.

My head flies backwards, hitting something soft. The ceiling spins, black clouding my vision, my eardrums ringing from the blast. As the world shudders to a stop, I realize I’m on the floor with Cole’s arms around me, his hand curled up to cradle my head.

I meet his eyes and find myself staring into pools of perfect black. His eyelids are open wide, unblinking, irises shrunk to thin blue rings. A vein pulses in his forehead, but his body is a statue, wrapped around me on the floor.

“Cole,” I say, grabbing his shirt, not sure he’s even breathing. “Cole!”

He shudders, sucking in a breath, and scrambles backwards.

“Cole, what the hell just happened?” I climb to my feet, shaking.

“I’m sorry,” he says. He scans the room, his pupils shrinking back to normal size. “I didn’t mean to do that, I’m sorry.”

“Jesus, Cole, your eyes.”

“Implants,” he mutters. He straightens his shirt, his gaze averted. He looks as stunned as I am. “They kick in when there’s danger. I don’t really control them.”

“Okay,” I say, steadying myself on the counter. My arm flickers with heat where his hand was. “Okay, I see that. But where the hell were you just then? You were like a machine.”

“I’m sorry,” he says again.

I rub my hands across my arms, tense with adrenaline, then my gaze drops to the screen below the box.

“No,” I whisper.

“What?”

“Two forty-five…” My mind races through the calculations. I jab them into the laptop to check, hands trembling. “No, no, no…”

“What, Catarina? Is it getting stronger?”

I turn from the laptop to the box, where fresh hairline cracks in the lid reflect the sunlight like mirrors, projecting jagged rainbows on the ceiling. The inside of the box is translucent pink, dripping as the bloodied mist condenses, but only the lid is broken. I grab my pen, climbing onto the counter, notching down today’s date on the horizontal axis and trace a line up, up, and above the trend lines to the top.

“I was wrong,” I whisper. I draw an X where the sample’s marker should be. “It’s even higher than this – the cracks absorbed some of the impact… but I’ve been doing this all wrong.”

I climb down slowly, staring at the cracked lid, the undamaged sides of the box. “It doesn’t go out,” I whisper, “it just goes up, so the cloud can spread further as it drifts.”

I scramble through the drawer for my notes, yanking them out, and spread them across the counter. Each test has been sketched, photographed and backed up on paper when I was able to. I line the images up quickly, watching the pattern emerge before my eyes.

“Talk to me,” Cole says, stepping to the counter.

“Okay, it’s the forces,” I whisper, “the dimensions, it’s all messed up.” I run a hand through my hair and point at the chart. “I told you the first thing Hydra did as it evolved was get stronger, right? That’s a variable – that’s the variable I’ve tested for, that I’ve designed this whole experiment around.”

“Sure.”

“But that’s not all it’s doing, it’s also becoming more focused. People always blow in a plume – they shoot up, right? Well, that plume is getting thinner, and it’s getting stronger. There are two variables, Cole, it’s a convolution, and it means I’ve messed up the radius calculation completely.”

Cole watches me, his eyes clouded. “If the same amount of energy is used in a more concentrated plume, it should go further, right?”

“Exactly,” I whisper. “People aren’t grenades anymore, Cole. Hydra’s turning them into guns.”

I scrawl an equation down on paper, accounting for the new variable, scribbling my observations into panicked calculus. I tap it into the computer, and suck in a breath as the true trend appears before me. I climb onto the counter and draw it with a trembling hand, the line smeared and jagged with nerves.

“It’s exponential,” Cole says.

I nod mutely, climbing down from the counter.

“How far will a cloud spread now?”

I glance at the ceiling, my mind ticking through the calculation. “Four miles, maybe, on a calm day.”

Cole’s eyes widen, the first flicker of true fear I’ve seen in him.

“But if this keeps going,” I whisper, “soon it’ll be into the cloud layer. When we hit winter and the snowstorms come, there won’t be anywhere left to hide.”