My sister Callie didn't kill herself so I could risk my future pulling stupid stunts. Yet here I am, hanging upside down over a cage of mice, while my best friend, Ryder Russell, anchors me with a rope and pulley as he squats in the air duct.

"If you drop me, I'll tell Mikey you snuck out of the compound last weekend," I say, too softly to set off the sensors inside the lab but loudly enough for Ryder to hear.

"If I drop you, my dad will be the least of our problems."

I stretch my fingers toward the metal cage, making sure my shirt stays tucked into my pants. I have a unique, blobby-hand birthmark at my waist, one I'd like to keep hidden from the security cameras. "A few more inches, and that should do it," I say.

Ryder grunts, and I fall half a foot.

My heart bounces as if it were attached to a bungee cord. But he won't drop me. He never has. This is our fourth time breaking into a lab, and we haven't made a mistake yet.

I swing my arms and reach for the cage door. Ryder and I bicker like brother and sister, but we're a team. From the time we were six years old and he gave me "first turns" with the mud puddles. He's like a cloud of gnats — always annoying and yet endearingly loyal. I'd never be able to do this without him.

One last swing, and I grab the latch. The cage is so big it runs the length of the counter. Inside, hundreds of white-furred, pink-nosed mice climb over one another, wriggle under the straw, and run through a three-level maze with bells and doors.

Below the latch, taped to the counter, is a photo ID. Even upside down, Tanner Callahan's straight brows and barely curved lips look cocky.

Of course they do. Tanner's sixteen, like me, but ever since he was a kid, the Technology Research Agency's been training him to become one of them: a scientist. I've heard rumors that his parents died in an accident, and he's grown up as an orphan within the walls of TechRA, adopted for all intents and purposes by a government organization.

Exaggeration? Maybe. But that doesn't mean he has to swagger around school like he's some kind of genius. Even if he kinda is.

I pry open the gate, setting off the silent alarm. The countdown begins. I have exactly one minute before the guards burst into the lab.

The mouse closest to me sniffs the air, as if testing the smell of freedom, and then clambers out of the cage. Another follows. And then another. Pretty soon, an avalanche of mice pours out of the opening and disappears behind the computer equipment and nests of wires.

Go on, little mice. Wriggle your way to a better life. Anything's better than being imprisoned here, day after day, at the mercy of scientists who treat your brain like a Petri dish.

I should know. That was me, ten years ago. Strapped to a reclining chair, hooked to a million sensors, forced to inhale chemical-laced fumes. If Callie hadn't broken into the Future Memory Agency, if my sister hadn't sacrificed herself to save me, I might still be there today.

Never again. If I can help it, no other living creature will be subject to the scientists' whims, either.

"All set," I say to Ryder. "Get me out of here."

The pulley creaks, and I inch up, up, up toward the ceiling. Victory, sweet and heady, floods my veins. We did it. We freed another cage of mice. There are dozens more cages just like this one, but at least these mice won't be studied. Will no longer be tortured. There's success in that.

I'm halfway to the ceiling when I notice him. A mouse, with his foot caught in the grating, half in, half out of the cage. The other mice scamper over him, their claws digging into his head as though he were just another obstacle.

The mouse pulls and tugs, but he can't get his leg loose. As the cage empties, his movements become more frantic, as if he realizes this is his last chance to escape. When he's the only one left, he flips his body around and attacks the caught leg with his teeth.

I suck in a breath. This must be one of the hyperintelligent mice I've heard about. He understands. He calculates. He weighs morality and makes decisions, just like us.

"Stop, Ry!"

The upward motion halts, and my teeth click together.

"What is it?" Ryder asks.

"A mouse is stuck. Lower me so I can help."

The rope jiggles. "The guards will be here in thirty seconds."

"He's about to gnaw off his leg. We have to help."

No response.

"Do it, Ry!"

I fall through the air so quickly I bump my head on the counter. I grit my teeth, ignoring the throbbing. I reach for the mouse instead. He turns and bites my hand, his teeth breaking through my glove and sinking into skin.

Ow. Lightning streaks across my brain, and I waste several moments blinking away the pain. This isn't the first time a mouse has bitten me. In fact, my gloves are all scratched up from the scrape of teeth. But it's the first time a bite has broken through their thick, protective material.

"Twenty seconds," Ryder says above me. "Come on, Jessa. The mouse isn't worth it. Leave him."

No way. I press two fingers on the mouse's jaw, wrap my hand around his torso, and pull.

Maybe I yank too hard. Or maybe the mouse had already gnawed through too much of his flesh. Whatever the reason, the leg separates from his body. And stays in the grating.

Shocked, I drop the mouse, and he hobbles away, his three legs scratching against the counter.

I stare at the detached leg. Furless, pink. The size of a matchstick. The skin is loose and bunched, the toes disproportionately long. Nausea roils in my stomach. My mouth dries, and I'm light-headed, but that could be from hanging upside down too long.

"Ten seconds," Ryder says. "Are you ready?"

I take a shuddering breath. Retreat first. Mourn later. "Yeah. Pull me up."

I fly through the air as if I'm on a zip line. Ryder grabs me under the arms and hauls me into the air duct, just as the lab door opens and half a dozen guards in navy uniforms spill into the room.

The ceiling panel is still uncovered, but a mechanical "spider" sits at the edge of the hole, projecting a holographic image that makes the surface appear smooth and uninterrupted.

I pull my knees to my chest and will myself not to move. Not to breathe. Not to look at the tiny severed limb stuck in the cage.

Oh Fates, I didn't mean to hurt him. The last thing I wanted was to rip off his leg. I was only trying to help.

In the dimness of the chute, I meet Ryder's eyes. His six-three frame is folded like origami, and the smooth darkness of his skin blends into the shadows. I read in his face the same emotion that compresses the walls of my throat. He saw the limb, too.

Below us, a strong voice cuts through the din. Through the holographic screen, Tanner pushes his way through the guards. His tousled black hair falls into his eyes, and he wears his bad-boy-scientist uniform — dark thermal shirt and cargo pants. Clothes just as appropriate for running lab experiments as for racing around on a hoverboard.

Here it comes. Tanner Callahan, boy genius, is about to throw a fit that will blow the spirals off this steel and glass building.

But he doesn't. Instead, he crouches in front of the cage and studies the leg. And then, with a gentleness even a precog couldn't have foreseen, he wiggles the limb loose and wraps it in a piece of white gauze.

I gape. He's not actually ... sad ... about the amputated leg? He...