IT IS COLD OUTSIDE, and still foggy in the low parts of the fields. I run straight until I reach the gardens’ grand front gate, which Thomas padlocked long ago. No one goes beyond the garden wall now. Before the war, the hospital wasn’t a hospital at all. It was the house of a beautiful, rich princess, only she was old, and you are probably thinking that doesn’t sound like a princess, but it’s true. When the bombs started, the princess went to live with relatives and gave the house to the Sisters of Mercy, who added more beds to all of the bedrooms and blacked out the windows with blankets, and the nuns came, and then children came, all on trains. Rumbling, rumbling, while the bombs burst outside. My neighbors were evacuated to Dorset on the first trains. They didn’t have the stillwaters. Benny does. Anna does. I do. All the children at Briar Hill hospital have the stillwaters, and so we are here, because we cannot infect each other because we are already infected.

Sister Mary Grace told me that when the princess lived here, the grounds were beautiful. Young men and women from as far as London would come to walk through the walled gardens, amid the rosebushes and statues and gurgling fountains. They used to throw open the ballroom doors so that music would pour onto the sprawling lawns, where her guests would play croquet. But the princess had an army of gardeners, and now we have only Thomas, and Thomas has only his one arm. So that is why the garden gate is locked, and why the little creeping briars grow longer and longer each day.

But the ivy forms a twisting ladder, and it is easy to climb over the garden wall. I just have to tuck my skirt between my legs. On the other side I drop down into a forgotten place. There are benches that are being slowly disappeared by honeysuckle, and crumbling statues of Greek gods with moss clinging to their faces. I wander the maze of walls and find a smaller garden, tucked away in the corner. There is a column in the center that reaches to my shoulders, and on top is a sundial. It has a circular base with a triangular arm pointing toward the sky to cast a shadow that tells the time. It looks to be made of gold or brass that might once have been reflective enough to show the mirror-horses, but now it’s too tarnished. I sit on a bench, crunching the vines, and blow into my hands.

Something rustles, and I go stiff.

I haven’t forgotten about the foxes.

I hold my breath so it won’t cloud in the air and give me away, and listen. There. More rustling, just around the corner. Something moving. Can that really be just a fox? And there. Back from the direction of the statues. The vines climbing the garden wall tremble suddenly, and I suck in a breath.

That is too big to be a fox.

I go completely still. Except for my breath. Except for my heart. Is this what Papa feels like on the front? That at any moment bullets might splinter the walls? That gas might cloud like morning fog?

Clomp.

I shriek. The ivy trembles violently. Should I run?

Clomp, CLOMP.

It’s getting closer! I drop down to the frozen earth. I crawl elbow over elbow through the trenches of dead grass. Benny told us a story once of a German plane that got lost in a storm and crashed on English soil. What if this is a German pilot, lost and angry? My heartbeat thunders in my chest. A willow branch snaps under my elbow, and I shriek.

Clomp, clomp, clomp.

It’s a German pilot, I know it, and he’s going to have a gun and he isn’t going to listen when I tell him I’m just a girl because he doesn’t speak English and he has no way of knowing I’m not a spy!

CLOMP.

He’s right around the corner now. There’s no time. I grab the snapped willow branch and brandish it, rising to my feet. Foxes or German pilots, Papa would be brave. I must be brave too.

A snort.

A heavy clomp, clomp, clomp.

A horse swivels its head around the corner. It is almost entirely white—it has long ropes of silken white mane, and a soft gray muzzle, and wings, snow-white wings, wings that are soft and giant and real.

I drop the willow branch.

“You aren’t a German soldier!” I cry.

The horse blinks.

“What are you?”

But I know what it is. Oh, I know.

Dry grass itches at my ankles and wind bites at my nose, but all I can do is stare at this horse. It’s from the mirror-world. But how did it cross over? And why? The winged horses never leave their world—they barely even glance at me when I tap on the hospital mirrors.

The horse takes a cautious step sideways, its dark eyes fixed on me.

I glance at the golden sundial, but even if it were still gleaming, the horse is much too large to have squeezed through it. And if it had climbed through any of the mirrors in the hospital, surely we would have heard the crash of broken glass. Perhaps it climbed up through the fountain’s reflective water—but no, the horse is not soaked with ice water.

Slowly, I press my hand to my mouth.

What if…what if it hasn’t crossed over into our world? What if I’ve crossed over into its world?

I pat my dress, my hair, the ivy. No, we are in our world. The sky is gray. The ground is gray. My clothes are gray. The world behind the mirror, I think, would not have so much gray.

The winged horse watches from across the garden, the frozen fountain between us. It snorts loudly, then tears the earth with a hoof the color of quicksilver. Rust-red soil rains against the briars. I think of how when Benny chases me, I run to the kitchen, where the table is an island that keeps him away.

But this horse is not Benny. It has powerful hooves. Powerful teeth. A fountain will not stop it.

I grab the willow branch, brandishing it again.

We stare each other down. My heart thunk-thunks, thunk-thunks, my mind spins. I cannot believe it is here. I cannot believe, even after watching its kind in the mirrors, that it is real.

It lets out another snort, breaking the standoff, and lurches forward. I clutch the willow branch like a sword, but it doesn’t attack. Its neck bends. It noses the fountain. Again. And again.

I lower the branch.

No, it is not a bloodthirsty creature out of one of Benny’s stories.

It is only trying to drink.

It looks at me, and I see more clearly this time. It is a girl. It’s something in her eyes, a gentleness. I can just tell.

The fountain doesn’t flow anymore, but frozen rainwater fills the basin. The horse paws, paws, paws, with her quicksilver hoof. There’s a blaze of dark hair between her eyes in the pattern of a star—no, a spark. A tingling feeling spreads through me. All this time, Sister Constance and Dr. Turner were wrong. The winged horses weren’t in my imagination. They’re real. She’s real. I want to run back to the hospital on winged feet and tell them all, yell it out, and bring them here….

But no.

No.

I remember Sister Constance’s face. Dr. Turner’s, too. And the whispers of the other children.

They did not believe me before, and they will not believe me now. That is okay. I am very good at keeping secrets, never mind what Benny says. And this secret—this horse—is my secret. Something just for me.

The horse paws again, muzzle nosing anxiously against ice. I take a step forward, cautiously, and raise the willow branch. The horse steps back, wary, like a deer at the edge of a wood. I use the branch to bust up the ice in the fountain, chop, chop, chop as hard as I can, and then step back quickly to the wall. My heart thunk-thunks. When I look at the horse, my mouth fills with the slightest, barely there taste of ash.

She takes a step forward. And another. Cautious. And then she lowers her head and drinks long and deep from the water beneath the ice. I think she is very thirsty, and that it has been a long time since she has drunk her fill.