The universe is in fact a multiverse. Countless quantum realities exist, all layered within one another; we’ll call these dimensions, for short.

Each dimension represents one set of possibilities. Essentially, everything that can happen does happen. There’s a dimension where the Nazis won World War II. A dimension where the Chinese colonized America long before Columbus ever sailed over. And a dimension where Brad Pitt and Jennifer Aniston are still married. Even a dimension just like my own, identical in every way, except on one day in fourth grade, that Marguerite chose to wear a blue shirt while I chose to wear a green one. Every possibility, every time fate flips a coin, splits the dimensions yet again, creating yet more layers of reality. It goes on and on forever, to infinity.

These dimensions aren’t off in faraway outer space. They’re literally all around us, even within us, but because they exist in another reality, we can’t perceive them.

Early in her career, my mom, Dr. Sophia Kovalenka, hypothesized that we should be able not only to detect those dimensions but also to observe them—even interact with them. Everyone laughed. She wrote paper after paper, expanded her theory year after year, and nobody would listen.

Then one day, just when it looked like she was going to get permanently written off as a crackpot, she managed to publish one more paper pointing out parallels between wave theory and her work on dimensional resonance. Possibly only one scientist on earth took that paper seriously—Dr. Henry Caine, an English oceanographer. And physicist. And mathematician. And, obviously, overachiever. When he saw the paper, he was able to grasp potential that nobody else had ever seen before in the theory. This was lucky for Mom, because once they became research partners, her work really started to go somewhere.

This was even luckier for Josie and me, because Dr. Henry Caine would become our dad.

Fast-forward twenty-four years. Their work had reached the point where it was starting to attract notice even outside scientific circles. The experiments in which they’d shown evidence of alternate dimensions had been replicated by other scientists at Stanford and Harvard; nobody was laughing at them anymore. They were ready to try traveling between dimensions—or, at least, to fashion a device that could make it possible.

Mom’s theory is that it would be very, very difficult for physical objects to move between dimensions, but energy should be able to move fairly easily. She also says consciousness is a form of energy. This led to all kinds of crazy speculation—but mostly Mom and Dad remained focused on building a device that would turn dimensional travel into more than a dream. Something that would allow people to journey to another dimension at will, and, even trickier, to come back again the same way.

This was daring. Even dangerous. The devices have to be made out of specific materials that move much more easily than other forms of matter; they have to anchor the consciousness of the traveler, which is apparently very difficult; and about a million other technical considerations I’d have to get umpteen physics degrees to even understand. Long story short: the devices are really hard to make. Which is why my parents went through several prototypes before even considering a test.

So when they finally had one that seemed like it would work, only a couple of weeks ago, we had to celebrate. Mom and Dad, who usually drink nothing stronger than Darjeeling, opened a bottle of champagne. Theo handed me a glass too, and nobody even cared.

“To the Firebird,” Theo said. The final prototype lay on the table around which we stood, its workings gleaming, intricate layers of metal folded in and atop each other like an insect’s wings. “Named after the legendary Russian creature that sends heroes on amazing quests and adventures”—here Theo nodded at my mother, before continuing—“and of course after my own muscle car, because yes, it’s just that cool.” Theo is a guy who says things like “muscle car” ironically. He says almost everything ironically. But there was real admiration in his eyes as he looked at my parents that night. “Here’s hoping we have some adventures of our own.”

“To the Firebird,” Paul said. He must have been plotting what he was going to do right then, even as he lifted his glass and clinked it against Dad’s.

Basically, after decades of struggle and ridicule, my parents had finally reached the point where they’d gained real respect—and they were on the brink of a breakthrough that would take them far beyond that. Mom would’ve been heralded as one of the leading scientists in all history. Dad would have gotten at least Pierre Curie status. We could maybe even have afforded for me to take a summer art tour in Europe, where I could go to the Hermitage and the Prado and every other amazing gallery I’d heard of but never seen before. Everything we’d ever dreamed of was on the horizon.

Then their trusted research assistant, Paul Markov, stole the prototype, killed my father, and ran.

He could have gotten away with it, slipping into another dimension beyond the reach of the law: the perfect crime. He vanished from his dorm room without a trace, leaving his door locked from the inside.

(Apparently when people travel between dimensions, their physical forms are “no longer observable,” which is a quantum mechanics thing, and explaining it involves this whole story about a cat that’s in a box and is simultaneously alive and dead until you open the box, and it gets seriously complicated. Never ask a physicist about that cat.)

Nobody could find Paul; nobody could catch him. But Paul didn’t count on Theo.

Theo came to me earlier this evening as I sat on the rickety old deck in our backyard. The only illumination came from the full moon overhead and the lights Josie had strung on the railing last summer, the ones shaped like tropical fish that glowed aquamarine and orange. I had on one of Dad’s old cardigans over my ivory lace dress. Even in California, December nights can be cold, and besides—the sweater still smelled like Dad.