A tiny black creature, no longer than Konstance’s pinkie nail, is climbing the wall. Its antennae wave; its leg joints extend, bend, extend again; the jagged tips of its mandibles would frighten her if they weren’t so small. She sets a finger in the creature’s path and it climbs aboard. It crosses her palm, proceeds to the back of her hand; the intricate complexity of its movements dazzles.

“Mother, look.”

The Perambulator whirs and pivots. Her mother, absorbed in another world, pirouettes, then extends her arms as though soaring.

Konstance presses her hand to the wall: the animal climbs off and continues along its original path, ascending past Father’s berth, until it disappears through the joint where wall meets ceiling.

Konstance stares. Behind her Mother flaps her arms.

* * *

An ant. On the Argos. Impossible. All the grown-ups agree. Don’t worry, Sybil tells Mother. It takes children years to learn the difference between fantasy and reality. Some longer than others.

* * *

She’s five. The ten-and-unders sit in a circle around the classroom Portal. Mrs. Chen says, “Sybil, please display Beta Oph2,” and a black-and-green sphere, ten feet in diameter, materializes in front of them. “These brown patches here, children, are silica deserts at the equator, and we believe that these are bands of deciduous forest in the higher latitudes. We expect that the oceans at the poles, here and here, will freeze over seasonally…”

Several of the children reach to touch the image as it rotates past, but Konstance keeps her hands pinned beneath her thighs. The green patches are beautiful, but the black ones—blank and serrated at the edges—frighten her. Mrs. Chen has explained that these are simply regions of Beta Oph2 that have not yet been mapped, that the planet is still too far away, that as they draw closer Sybil will take more detailed images, but to Konstance they look like chasms a person could fall into and from which a person could never escape.

Mrs. Chen says, “Planetary mass?”

“One-point-two-six Earth masses,” recite the children.

Jessi Ko pokes Konstance’s knee.

“Nitrogen in the atmosphere?”

“Seventy-six percent.”

Jessi Ko pokes Konstance’s thigh.

“Oxygen?”

“Konstance,” whispers Jessi, “what’s round, on fire, and covered with trash?”

“Twenty percent, Mrs. Chen.”

“Very good.”

Jessi leans halfway into Konstance’s lap. Into her ear she hisses, “Earth!”

Mrs. Chen glares in their direction and Jessi straightens and Konstance feels heat rush to her cheeks. The image of Beta Oph2 rotates above the Portal: black, green, black, green. The children sing:

You can be one,

Or you can be one hundred and two,

It takes everyone together,

Everyone together,

to get to Beta Oph2.

* * *

The Argos is an interstellar generation ship shaped like a disk. No windows, no stairs, no ramps, no elevators. Eighty-six people live inside. Sixty were born on board. Twenty-three of the others, including Konstance’s father, are old enough to remember Earth. New socks are issued every two mission years, new worksuits every four. Six two-kilo bags of flour come out of the provision vaults on the first of every month.

We are the lucky ones, the grown-ups say. We have clean water; we grow fresh food; we are never ill; we have Sybil; we have hope. If we allocate carefully, everything we have with us is everything we will ever need. Anything we cannot solve for ourselves, Sybil will solve for us.

Most of all, the grown-ups say, we must mind the walls. Beyond the walls waits oblivion: cosmic radiation, zero gravity, 2.73 Kelvin. In three seconds outside the walls, your hands and feet would double in size. The moisture on your tongue and eyeballs would boil away, and the nitrogen molecules in your blood would clump together. You’d suffocate. Then you’d freeze solid.

* * *

Konstance is six and a half when Mrs. Chen brings her, Ramón, and Jessi Ko to see Sybil in person for the first time. They arc down corridors, past the Biology Labs, past the doors to Compartments 24, 23, and 22, curling inward toward the center of the ship, and step through a door marked Vault One.

“It’s very important that we don’t bring in anything that might affect her,” says Mrs. Chen, “so the vestibule will clean us. Shut your eyes, please.”

Outer door sealed, announces Sybil. Beginning decontamination.

From somewhere deep inside the walls comes a sound like fans accumulating speed. Chilled air whooshes through Konstance’s worksuit and a bright light pulses three times on the other side of her eyelids and an inner door sighs open.

They step into a cylindrical vault fourteen feet across and sixteen feet high. At the center, Sybil hangs suspended inside her tube.

“So tall,” whispers Jessi Ko.

“Like a gatrillion golden hairs,” whispers Ramón.

“This vault,” says Mrs. Chen, “has autonomous thermal, mechanical, and filtration processes, independent of the rest of the Argos.”

Welcome, says Sybil, and pinpricks of amber go fluttering down her tendrils.

“You’re looking lovely today,” says Mrs. Chen.

I adore visitors, says Sybil.

“Inside there, children, is the collective wisdom of our species. Every map ever drawn, every census ever taken, every book ever published, every football match, every symphony, every edition of every newspaper, the genomic maps of over one million species—everything we can imagine and everything we might ever need. Sybil is our guardian, our pilot, our caretaker: she keeps us on course, she keeps us healthy, and she safeguards the heritage of all humanity against erasure and destruction.”

Ramón breathes on the glass, puts a finger to the vapor, and draws an R.

Jessi Ko says, “When I’m old enough to go to the Library, I’m going straight to the Games Section to fly around Flower-Fruit Mountain.”

“I’m going to play Swords of Silverman,” says Ramón. “Zeke says it goes on for twenty thousand levels.”

Konstance, Sybil asks, what will you do when you get to the Library?

Konstance glances over her shoulder. The door they entered through has sealed so tightly behind them that it is indistinguishable from the wall. She says, “What’s ‘erasure and destruction’?”

* * *

Night terrors come next. After Third Meal is cleaned up, after the other families retire to their compartments, after Father heads back to his plants in Farm 4, Mother and Konstance walk back to Compartment 17 and tidy the various worksuits waiting their turn at Mother’s sewing machine—here the bin for malfunctioning zippers, here the bin of scraps, here the loose threads, nothing wasted, nothing lost. They powder their teeth and brush their hair and Mother takes a SleepDrop and kisses Konstance on the forehead and they climb into their respective berths, Mother on the bottom and Konstance on the top.

The walls dim from purple to gray to black. She tries to breathe, tries to hold her eyes open.

Still they come. Beasts with glittering razor-teeth. Slavering devils with horns. Eyeless white larvae swarming inside her mattress. The worst are the ogres with skeleton limbs that come scuttling down the corridor; they tear open the compartment door, climb the walls, and chew through the ceiling. Konstance clings to her berth as her mother is sucked out into the void; she tries to blink but her eyes are boiling; she tries to scream but her tongue has turned to ice.