MY HAND SHAKES AS I BRACE MYSELF AGAINST THE BRICK wall. Rain falls cold and sharp against my skin, from a sky I’ve never seen before. It’s hard to catch my breath, to get any sense of where I am. All I know is that the Firebird worked. It hangs around my neck, still glowing with the heat of the journey.

There’s no time. I don’t know whether I have minutes, or seconds, or even less. Desperately I tug at these unfamiliar clothes—the short dress and shiny jacket I wear have no pockets, but there’s a small bag dangling from my shoulder. When I fish inside, I can’t find a pen, but there’s a lipstick. Fingers trembling, I unscrew it and scrawl on a tattered poster on the wall of the alley. This is the message I must pass on, the one goal I have to remember after everything else I am is gone.

Then I can only wait to die.

Die isn’t the right word. This body will continue to breathe. The heart will continue to beat. But I won’t be the Marguerite Caine living in it anymore.

Instead, this body will return to its rightful owner, the Marguerite who actually belongs in this dimension. The dimension I leaped into, using the Firebird. Her memories will take over again, any second, any moment, and while I know I’ll awaken again in time, it’s terrifying to think about . . . passing out. Getting lost. Being trapped inside her. Whatever it is that happens to people traveling from another dimension.

It hits me then. The Firebird really works. Travel between alternate dimensions is possible. I just proved it. Within my grief and fear, one small ember of pride glows, and it feels like the only heat or hope in the world. Mom’s theories are true. My parents’ work is vindicated. If only Dad could have known.

Theo. He’s not here. It was unrealistic of me to hope he would be, but I hoped anyway.

Please let Theo be all right, I think. It would be a prayer if I still believed in anything, but my faith in God died last night too.

I lean against the brick wall, hands spread like a suspect’s on a police car right before the cuffs go on. My heart hammers in my chest. Nobody has ever done this before—which means nobody knows what’s about to happen to me. What if the Firebird can’t bring me back to my own dimension?

What if this is how I die?

This time yesterday, my dad probably asked himself that same question.

I close my eyes tightly, and the cold rain on my face mingles with hot tears. Although I try not to picture how Dad died, the images force their way into my mind over and over: his car filling with water; brownish river lapping over the windshield; Dad probably dazed from the wreck but scrambling to get the door open, and failing. Gasping for the last inches of air in the car, thinking of me and Mom and Josie—

He must have been so scared.

Dizziness tilts the ground beneath my feet, weakens my limbs. This is it. I’m going under.

So I force my eyes open to stare at the message again. That’s the first thing I want the other Marguerite to see. I want that message to stay with her, no matter what. If she sees that, if she keeps running over those words in her mind, that will awaken me within her as surely as the Firebird could. My hate is stronger than the dimensions, stronger than memory, stronger than time. My hate is now the truest part of who I am.

The dizziness builds, and the world turns fuzzy and gray, blackening the words KILL PAUL MARKOV—

—and then my vision clears. The word KILL sharpens back into focus.

Confused, I step back from the brick wall. I feel wide awake. More so than before, actually.

And as I stand there, staring down at my high heels in a puddle, I realize that I’m not going anywhere.

Finally, as I begin to trust my luck, I step farther into the alley. The rain beats down harder on my face as I look up into the storm-drenched sky. A hovercraft looms low over the city like yet another thundercloud. Apparently it’s there to fly holographic billboards across the city skyline. Astonished, I gaze at the hovercraft as it soars through this strange new dimension, 3D advertisements flickering through their motions in the sky around it: Nokia. BMW. Coca-Cola.

This is so like my world, and yet not my world at all.

Is Theo as overwhelmed by the journey as I am? He must be. His grief is nearly as deep as mine, even though Dad was only his adviser; more than that, this is what Theo and my parents worked for these past few years. Has he kept his memory as well? If so, we’ll be in control throughout the trip, our minds piloting the selves born in this alternate dimension. That means Mom was wrong about one thing—which is kind of staggering, given that every other theory she’s ever had has just been proved true. But I’m grateful for it, at least for the moment before my gratitude disintegrates in the hot blaze of anger.

Nothing can stop me now. If Theo made it too and he can find me—and I want so desperately for him to find me—then we’ll be able to do this. We can get to Paul. We can take back the Firebird prototype he stole. And we can take our revenge for what he did to my father.

I don’t know if I’m the kind of person who can kill a man in cold blood. But I’m going to find out.

I’M NOT A PHYSICIST LIKE MOM. NOT EVEN A GRAD STUDENT in physics like Paul and Theo. I’m the homeschooled daughter of two scientists who gave me a lot of leeway to direct my own education. As the only right-brained member of the family, I wound up pursuing my passion for painting a whole lot more than I ever studied higher-level science. In the fall, I’m headed to the Rhode Island School of Design, where I’m going to major in art restoration. So if you want to mix oil paints, stretch a canvas, or discuss Kandinsky, I’m your girl. The science underlying cross-dimensional travel? No such luck. But here’s what I know: