The herd had crested the rise; Peter watched from above as they approached, a jostling, bleating mass that flowed like liquid up the hill, followed by the riders, six in all, tall on their mounts. The herd moved as one toward him through the gap in the fireline, their hooves kicking up a cloud of dust. As the riders passed under his post, each gave Peter a tight nod of acknowledgment, as they had for each of the last six evenings.

No words would pass between them. It was bad luck, Peter knew, to speak to someone waiting on the Mercy.

One of the riders broke away: Sara Fisher. Sara was a nurse by trade; Peter's own mother had been the one to train her. But like many people, she had more than one job. And Sara was built to ride-slender but strong, with an alert physical presence in the saddle and a quick, supple style on the reins. She was dressed, as all the riders were, in a loose jersey cinched at the waist, above leggings of patched denim. Her hair, a sun-warmed blond cut short to the shoulders, was tied away, a single loose strand swaying over her eyes, deep-set and dark. A leather bow guard sheathed her left arm from elbow to wrist; the bow itself, a meter long, was slung diagonally across her back like a single jouncing wing. Her horse, a fifteen-year-old gelding known as Dash, was said to prefer her above all others, pinning his ears and flicking his tail at anyone else who attempted to ride him. But not Sara; under Sara's command he moved with a responsive grace, horse and rider seeming to share each other's thoughts, becoming one.

As Peter watched, she cut through the gate again, against the current, back onto open ground. He saw what had drawn her away: a single lamb, a cosset born in spring, had wandered off, diverted by a patch of summer grass just inside the fireline. Setting her horse square to the tiny animal, Sara swung to the ground and in a burst of dexterous motion rolled the lamb onto its back, roping its legs three times around. The last of the herd was passing through the gate now, a roiling wave of horses and sheep and riders heading down the trace that followed the curve of the west wall toward the pens. Sara straightened and lifted her face toward the place where Peter stood on the catwalk; their eyes met quickly across the gap. On any other occasion, he thought, she would have smiled. As Peter looked on, she hoisted the lamb to her chest and draped it across the horse's back, holding it in place with a steadying hand while she swung up into the saddle. A second meeting of the eyes, long enough to hold a sentence: I hope Theo doesn't come, either. Then, before Peter could consider this further, Sara flicked her heels and rode briskly through the gate, leaving him alone.

Why did they do it? Peter wondered-as he had wondered through all the nights he'd stood. Why did they come home, the ones who'd been taken up? What force drove the mysterious impulse to return? A last, melancholy memory of the person they'd once been? Did they come home to say goodbye? A viral, it was said, was a being without a soul. When Peter had turned eight and been released from the Sanctuary, it was Teacher, whose job this was, who had explained all of this to him. In its blood was a tiny creature, called a virus, that stole the soul away. The virus entered through a bite, typically to the neck but not always, and once it was inside a person, the soul was gone, leaving the body behind to walk the earth forever; the person they had been was no more. These were the facts of the world, the one truth from which all other truths descended; Peter might just as well have been wondering what made the rain fall; and yet, standing on the catwalk in the sharpening dusk-the seventh and final night of the Mercy, after which his brother would be declared dead, his name etched into the Stone, his belongings carted off to the Storehouse to be patched and repaired and redistributed at Share-he thought it. Why would a viral come home if it had no soul?

The sun stood just one hand above the horizon now, descending quickly into the wavy line where the foothills declined to the valley floor. Even in high summer the days seemed to end this way, in a kind of plunge. Peter cupped his eyes against the glare. Somewhere out there-past the fireline, with its loose jumble of felled timber, and the grazing grounds of Upper Field and the dump with its pit and piles, and the scrubby woodlands hills beyond-lay the ruins of Los Angeles and, farther still, the unimaginable sea. When Peter was a Little and still living in the Sanctuary, he had learned about this, in the library. Although it had been decided, long ago, that most of the books the Builders had left behind were of no value, and potentially confusing to the Littles, who were not to know anything about the virals or what had happened to the world of the Time Before, a few were allowed to remain. Sometimes Teacher would read to them, stories about children and fairies and talking animals who lived in a forest behind the doors of a closet, or else allow them to select a book on their own, to look at the pictures and read as best they could. The Oceans Around Us: that had been Peter's favorite, the book he'd always chosen. A faded volume, its pages dank-smelling and cool to the touch, the cracked binding held together by bits of curling yellow tape. On the cover was the name of the author, Ed Time-Life, and inside, page after wondrous page of pictures and photos and maps. One map was called the World, which was everything, and most of the World was water. Peter asked Teacher to help him read the names: Atlantic, Pacific, Indian, Arctic. Hour after hour he sat on his mat in the Big Room, the book cradled in his lap, turning the pages, his eyes locked onto these blue spaces on the maps. The World, he gathered, was round, a great watery ball-a dewdrop hurtling through the sky-and all the water was connected. The rains of spring and snows of winter, the water that poured from the pumps, even the clouds above their heads-that was all part of the oceans, too. Where was the ocean? Peter asked Teacher one day. Could he see it? But Teacher only laughed, as she always did when he asked too many questions, dismissing his concerns with a shake of her head. Maybe there's an ocean and maybe there isn't. It's only a book, Little Peter. Don't you go worrying about oceans and such.

But Peter's father had seen the ocean: his father, the great Demetrius Jaxon, Head of the Household, and Peter's uncle Willem, First Captain of the Watch. Together they'd led the Long Rides farther than anyone had ever gone, since before the Day. Eastward, toward the morning sun, and west to the horizon line and farther still, into the empty cities of the Time Before. Always his father returned with stories of the great and terrible sights he'd seen, but none was more wondrous than the ocean, in a place he called the Long Beach. Imagine, Peter's father told the two of them-for Theo was there as well, the two Jaxon brothers sitting at the kitchen table of their small house in the hour of their father's return, raptly listening, drinking his words like water-imagine a place where the ground simply stopped, and beyond that place an endless tumbling blueness, like the sky turned upside down. And sunk down in it, the rusting ribs of great ships, a thousand thousand of them, like a whole drowned city of man's creation, jutting from the ocean's waters as far as the eye could see. Their father was not a man of words; he communicated only with the most sparing phrases and parceled his affections the same way, letting a hand on a shoulder or a well-timed frown or, in moments of approval, a terse nod from the chin do most of his speaking for him. But the stories of the Long Rides brought out the voice in him. Standing on the ocean's edge, his father said, you could feel the bigness of the world itself, how quiet and empty it was, how alone, with no man or woman to look at it or say its name through all the years and years.

Peter was fourteen when his father returned from the sea. Like all the Jaxon males, including his older brother, Theo, Peter had apprenticed to the Watch, hoping someday to join his father and uncle on the Long Rides. But this never happened. The following summer, the scouting party was ambushed in a place his father called Milagro, deep in the eastern deserts. Three souls lost, including Uncle Willem, and there were no more Long Rides after that. People said that it was his father's fault, that he had gone too far, taken too many chances, and for what? None of the other Colonies had been heard from in years; the last, Taos Colony, had fallen almost eighty years ago. Their final transmission, back before the Separation of the Trades and the One Law, when radio was still permitted, said their power plant was failing, the lights were going out. Surely they'd been overrun like all the others. What was Demo Jaxon hoping to accomplish, leaving the safety of the lights for months at a time? What did he hope to find, out there in the dark? There were those who still spoke of the Day of Return, when the Army would come back to find them, but never in all his travels had Demo Jaxon found the Army; the Army was no more. So many men dead now, to learn what they already knew.

And it was true that from the day Peter's father returned from the last Long Ride, there was something different about him. A great weary sadness, as if he'd leapt abruptly forward in age. It was as if a part of him had been left in the desert with Willem, whom Peter knew his father loved most of all, more than Peter or Theo or even their mother. His father stepped down from the Household, passing his seat to Theo; he began to ride alone, leaving with the herds at first light, returning just minutes before Second Evening Bell. He never told anyone where he went, as far as Peter knew. When he asked his mother, all she could say was that his father was in his own time now. When he was ready, he would return to them.

The morning of his father's final ride, Peter-a runner of the Watch by this time-was standing on the catwalk near Main Gate when he saw his father preparing to leave. The lights had just gone down; Morning Bell was about to sound. It had been a quiet night, without sign, and for an hour before dawn, a light snow had fallen. The day broke slowly, gray and cold. As the herd was gathering at the gate, Peter's father appeared on his mount, the great roan mare he always rode, headed down the trace. The horse was called Diamond because of the marking on her brow, an orphaned splash of white beneath the swishing mask of her long forelock; not an especially fast mount, his father always said, but loyal and tireless, and quick when you needed her to be quick. Now, watching his father holding her reins, standing at the rear of the herd while he waited for the gate to open, Peter saw Diamond do a little quickstep, tamping down the snow. Jets of steam puffed from her nostrils, swirling like a wreath of smoke around her long, self-possessing face. His father bent low and stroked the side of her neck; Peter saw his lips moving as he whispered something, some gentle encouragement, into her ear.

When Peter thought of that morning, five years ago, he still wondered if his father had known he was there, observing him from the snow-slickened catwalk. But he had never lifted his eyes to find him, nor had Peter done anything to alert his father to his presence. Watching him as he spoke to Diamond, stroking the side of her neck with his calming hand, Peter had thought of his mother's words, and knew them to be true. His father was in his own time now. Always, in the last moments before Morning Bell, Demo Jaxon would retrieve his compass from his waist pouch and open it once to examine it, then snap it closed as he called his head count to the Watch: "One out!" he would call, in his deep, barrel-chested voice. "One back!" the gatekeeper would reply. Always the same ritual, meticulously observed. But not that morning. It was only after the gates had opened and his father had passed, taking Diamond down the power station road, away from the grazing fields, that Peter realized his father had carried no bow, that the sheath at his belt was empty.

That night, Second Bell rang without him. As Peter would soon learn, his father had taken water at the power station midday and was last seen heading out under the turbines, into open desert. It was generally held that a mother could not stand for one of her own children, nor a wife for a husband; though nothing was written, the job of the Mercy had naturally fallen to a chain of fathers and brothers and eldest sons, performing this duty since the Day. So it was that Theo had stood for their father, as Peter now stood for Theo-just as someone, perhaps a son of his own, would stand for Peter should that day come.

Because if the person wasn't dead, if they'd been taken up, they always came home. It might be three days or five or even a week, but never longer than that. Most were Watchers, taken on scavenging parties or trips to the power station, or else riders with the herd or the Heavy Duty crews, who went outside to log or do repairs or drag garbage to the dump. Even in broad daylight, people were killed or taken; you were never really safe as long as the virals had shade to move in. The youngest homecomer that Peter knew of had been the little Boyes girl-Sharon? Shari?-nine years old when she was taken up on Dark Night. The rest of her family had been killed outright, either in the quake itself or the attack that followed; with no one left to stand for her, it had been Peter's uncle Willem, as First Captain, who had done this awful job. Many, like the Boyes girl, were fully taken up by the time they returned; others appeared in the midst of their quickening, sick and shuddering, tearing the clothing from their bodies as they staggered into view. The ones furthest along were the most dangerous; more than one father or son or uncle had been killed in this manner. But generally they offered no resistance. Most just stood there at the gate, blinking into the spotlights, waiting for the shot. Peter supposed that some part of them still remembered being human well enough to want to die.

His father never returned, which meant he was dead, killed by the virals out in the Darklands, at a place called Milagro. Their father had claimed he'd seen a Walker there, a solitary figure darting in the moonlit shadows, just before the virals attacked. But by that time, with the Household and even Old Chou having turned against the Long Rides, and Peter's father in disgrace, having resigned to pursue his mysterious, solitary expeditions without the Wall-moving in the expanding orbit that even then had seemed to Peter a rehearsal for something final-no one had believed him. A claim as bold as that: surely it was just Demo Jaxon's desire to continue the rides that made him claim something so absurd. The last Walker to come in had been the Colonel, almost thirty years ago, and he was an old man now. With his great white beard and wind-bit face, brown and thickened as tanned hide, he seemed nearly as old as Old Chou, or even Auntie herself, Last of the First. A single Walker, after all these years? Impossible.