If the Home Office versions of my parents and Wyatt Conley were willing to destroy entire dimensions to get Josie back, they’d think nothing of asking one person from their own world to die too. For a moment it hit me with dizzying force: Literally trillions of lives were at stake, and I was the only person with the power to save them. But I held on. “Wait. Wouldn’t the universe’s destruction slingshot her home? That’s what your Home Office selves think will happen to the splinters of Josie’s soul.”

Dad nodded. He looked as if he’d aged five years in an hour. “That’s probably what would happen to a perfect traveler—you or the Home Office’s Josie—but not to your other self or to anyone else trying to destroy a universe with a Firebird. That destruction has consequences. It forges chains. It’s as if . . . as if you were freeing a ship from anchor, but the only way to do it was by taking hold of that anchor yourself. While the ship sails free, the anchor drags you down to the bottom of the ocean. A perfect traveler would be able to overcome that, with the Firebird’s help. But anyone else would be done for.”

As unnerved as my parents were at the prospect, I felt slightly reassured. Maybe that should’ve embarrassed me—the fact that I could kind of handle the idea of an entire universe’s death if I knew I could escape. But traveling between dimensions involved enough danger already; any protection at all made me feel safer. So I let my parents show me how to use the Firebird to stabilize a universe. I refused to learn how to destroy one, because that was not a thing I was ever, ever going to do. Paul remained nearby, grave and quiet, still not looking me in the face.

It was Theo who raised a question I hadn’t considered. “Are you even going to be able to follow her?”

“What do you mean?” I said.

“If she’s not in her own dimension, then she’s already occupying a version of her in another world. Can two people leap into the same host?” He shrugged. “Seriously, no clue.”

Mom made a face. “I knew we ought to have run simulations on that.”

It didn’t seem like a big deal. Either I’d be able to do it or I wouldn’t, and if I could, I’d be in charge, because I was the perfect traveler, not Wicked. Then a ghastly possibility occurred to me. “We wouldn’t, like, fuse together or something, would we?”

At once, all four of them said, “No.” Dad helpfully added, “Different resonances, no matter what. Like oil and water, sweetheart.”

Good. I could imagine Wicked’s malevolence covering me like an oil slick, viscous and black. Better that than carrying it inside me. “You guys—remember what I told you about the Cambridgeverse?”

It took them a minute. I didn’t blame them. The story of my last chase through the dimensions was one I’d told in a rush while blood was still gushing from Paul’s arm. Paul winced at the mention of the place, because that was the world where he’d damaged my arm in a car crash that tore us all apart. But the most important aspect of the Cambridgeverse was something else entirely.

“Our counterparts are working on communicating through the dimensions,” Mom said. “You told them to reach out to us. Which means we’re poised to reach back.”

“We considered this, early on,” Dad mused, rubbing his chin in the way that meant he was either deep in thought or listening to Rubber Soul.

“If you could let them know what’s about to happen, to look out for Triad, it would give them a chance.” I looked at my torn, bloody clothing and, absurdly, felt like I ought to change before I went. When I returned home after all this and my body became observable once more, would the blood have dried? Or would it still be wet against my skin, proof of how my hands had hurt Paul?

She could’ve gone for his throat. What would I have done if I’d had to watch myself murder him?

Paul broke into my reverie, saying, “Are you ready?”

“No. But it doesn’t matter.” I reached up—he’s so tall, so heavily muscled, a Michelangelo in a world of Modiglianis. Still, I could cradle his face with my hands. “Follow me. I need all the help I can get.”

He hesitated from fear—not for himself. “Theo could go, or Sophia and Henry could finally use the Firebird for themselves—”

I whispered, “I need you.”

Paul didn’t believe me. He couldn’t, yet. But he nodded, and that had to be enough.

So I backed up, sat down in a far chair in the corner, hit the Firebird’s controls to leap after Wicked—

—and that’s why I’m now hanging from a cable about four hundred feet over the river Thames.

“Marguerite!” Paul shouts. I glance back to see him sliding out the observation window despite the cries of dismay from people nearby. My Aunt Susannah leans forward, her tears tracing streaks of mascara down her cheeks. Paul yells, “I’m going to come get you.”

“Don’t!” It costs me to shout that, because oh, God, I want him to come get me. I want him to save me. And from the glint of metal around his neck, I know this is my Paul—that he followed me, that as damaged as he is, at least something inside him still believes we can make it.

But I’m pretty sure he can’t save me. He’ll only get himself killed.

My sweaty palms slip against the cable; my fingers cramp so hard it’s like every nerve and bone is on fire. If I let go, the Londonverse Marguerite will die.

She was the first alternate self I ever entered, the first time I had to interpret the life I would’ve led in an alternate world. I think of her white, empty room. Her party-girl existence that she doesn’t enjoy a moment of. When I last stood inside her, I willed her to remember our parents—the ones robbed from her in childhood, the ones whose love I was able to share with her, at least a little. Now I know she kept those memories. She came out with Aunt Susannah to do something fun, and Paul Markov seems to have found her. Are they only friends, or something more? Regardless, he must be one of the only honest, real people in her life.

In other words—during the past few months, her life has been worth living. Now Wicked has taken it away.

That’s what they mean by “slamming doors,” I realize. They know now I’ll never do what they want. So they want to keep me from protecting these universes. The only way they can do that is by locking me out, forever.