Romola gives me directions. Most of the landmarks she names are unknown to me (Via Flaminia?), but she points along the road. I thank her and wave as I start running again.

At home, I think I could run a few miles without getting winded. This Marguerite doesn’t seem to get as much exercise. A stitch makes my gut clench; my breaths are coming too fast. Despite the cool air of early April, sweat slicks my skin. These thick woolen clothes feel as if they’re loaded with weights. And my boots—let’s just say shoemaking technology is a whole lot better at home. The blisters already swell at my heel and toes.

But I have to reach Paul as fast as I can. He could be in terrible danger—

Or he could be fine. Maybe he’s one of the castle guards. He could even be a prince! You’ll probably interrupt him at a banquet or something.

How long has he been here? We tried not to panic when he hadn’t returned to our dimension after twenty-four hours; after forty-eight hours, we all knew something was wrong. We got really afraid when we searched for him in the Triadverse and realized he’d left but hadn’t come back home. Mom and Theo outdid themselves, coming up with a way to trace Paul’s next leap, which was into this dimension.

Paul had no reason to come here. If he’d found what he was looking for—the cure for Theo—he would have come straight home. That was how we knew he’d been kidnapped. I haven’t been able to sleep since.

Just get him back. We’ll figure the rest out later—how to save Theo, how to defeat Triad. That can all wait until you bring Paul home.

I know the Castel Sant’Angelo as soon as I see it: an enormous stone structure at the top of a hill, lit by blazing torches. The firelight reveals the dull black gleam of cannons jutting from slots in the masonry. As I walk up, I see that the palace guards wear outfits simultaneously hilarious and intimidating: full striped breeches, brilliant yellow coats with puffy sleeves, metal breastplates and helmets, and swords that look like they could run through a human being in an instant. Although the soldiers come to attention as I step closer, obviously a winded teenage girl isn’t their idea of a threat.

What if Paul’s a prisoner here? I have no idea how the guards are going to react, but there’s only one way to find out. A couple of deep breaths, and then I say as firmly as I can manage, “I’ve come to speak to Paul Markov of Russia.”

The guards look at each other and say nothing. Crap. Should I have called him Paolo, the Italian version of the name? Or Pavel, the Russian version? Or maybe he is a prisoner—or he isn’t actually here at all—

“Follow me,” says one of the guards. “You can wait in the usual room.”

The usual room? I have to stifle a smile as I follow them to a small, stone-walled chamber. Of course Paul and I know each other in this world too.

Always, we find each other.

In my world, Paul is one of my parents’ research assistants as he works on his doctorate at Berkeley. For the first year and a half I knew him, I mostly thought he was strange: silent, awkward, too big for any room he was in. When he did speak, he was blunt. Most of the time he didn’t speak at all. But as time went on, I began to realize that his bluntness wasn’t him being rude or unkind—that instead it was a rough kind of honesty, sometimes hard to hear but always true. His awkwardness was only shyness, Paul’s belief that he had never fit in anywhere and never would. And the way he hung around my parents’ house wasn’t because he had no life and nowhere else to go. It was because nobody had ever accepted him before. He’d never been around a family who cared about each other, never had a real friend before he met my parents’ other assistant, Theo.

And he had never fallen in love before he knew me. He just didn’t know how to say it.

I’ve visited a few dozen dimensions by now. Paul and I have known each other in most of them; in many, we’re already together. Fate and mathematics bring us to each other time after time. Paul’s doctoral thesis presents a series of equations that prove destiny is real . . . but I don’t need the math to convince me. I’ve seen it for myself so many times, beginning in a Russia where the tsars never fell.

For a moment I think of Lieutenant Markov, the Paul I knew there, and my throat tightens. But that’s when a figure in a dark cloak appears in the stone archway of the room.

Paul steps forward, looking at me so sadly that I ache for him without even knowing why. “You know you should not have come,” he says softly.

“I had to.”

Bluffing your way through alternate dimensions can sometimes be tricky. When in doubt, remain silent as long as you can, and let the natives do the talking.

And right now I’m only speaking to this world’s Paul. A few cues tip me off to the differences—subtle things anyone else might miss, like the way he walks, or his ease in this medieval chamber. My Paul’s consciousness—his soul—must be within this body, but semiconscious, unable to act, unable to think, hardly even able to remember. For the time being, he’s forgotten himself. That’s what happens to most people when they travel through the dimensions: they become absorbed into their other selves, unable to escape, or even think that they should escape.

It’s like a fairy tale in reverse. The prince is the one asleep in a glass coffin. I’m the one who’ll awaken him.

If only a kiss would work.

Paul steps closer to me, and the flickering lanterns paint his face in golden light. He’s a big man, almost intimidatingly so—six foot two and broad-shouldered. This version isn’t as powerfully muscled, or maybe I just can’t tell beneath the black robes he wears.

Wait. Are these priest’s robes?

“I have prayed and prayed,” Paul whispers. His gray eyes search mine, and I wish I didn’t recognize how lost he looks. How alone. “Surely I cannot abandon the vows I made to God. And yet if he did not want me to marry as other men do—to feel desire, and love—why would he have brought me to you?”

Even without knowing any more of the story, this is enough to make me melt. This world’s Marguerite must be as in love with him as he is with her, or else they wouldn’t have had this conversation before. That makes it okay for me to say, “We’re brought together by a power greater than either of us. Something bigger than our own world.”

It’s not just a romantic saying; it’s scientific fact.

Paul breathes out heavily like a man struggling. I wonder what his life has been like here—born in Russia, surely. Back in the Middle Ages, lots of children were more or less given to the church when they were small, so they had no real choice about whether to enter the priesthood or convent or whatever; if Paul’s already taken vows one month after his twentieth birthday, that must be what happened to him. Perhaps he traveled to Rome to serve the pope. Then he met the inventors’ daughter, and everything changed.

I hope this world’s Paul and Marguerite will get their chance to be together. At any other time, I’d be tempted to stay here longer and help if I could. For now, though, nothing matters as much as rescuing my Paul and bringing him home.

“Paul?” I step closer to him. The firelight catches the faint reddish tint in his pale brown hair. “Come here.”

“We shouldn’t,” he says, like a man who desperately wishes we would.