Nico talks for a while, and I listen as best I can, but a lot of it just washes over me, a lot of it is just words. There's a rogue scientist, of course: Hans-Michael Parry, an astrophysicist formerly associated with the United States Space Command, who knows exactly how to do it, knows where these specially constructed fuses are housed and how they are operated. Nico's organization has found Parry in a military prison, and they're going to get him over to England, where sympathetic elements are ready to try this deflection maneuver with British bombs.

"Oh," I say, during this exegesis, over and over, just: "Okay." I pat my lap and Houdini clambers up. I scratch him behind the ears, mutter "that's a boy" before he escapes to chase a stray bit of kibble across the room.

There was a part of me, I realize as she's speaking, that wanted to be surprised. I wanted her to say something that would make me say Holy moly! She's right! But of course that was never really possible, was it? That, of all the people in the world, my sister is going to happen to be the one with a solution. No one has a solution. No one sitting in India Garden, no maverick astrophysicist rotting in the bowels of the U.S. Army prison system. It's all nonsense, so plainly so that it would be hilarious if I didn't know of at least one person who had already been sacrificed to my sister's belief that it's real.

"So what?" I finally ask. "You and your friends are going to spring this scientist from the pokey?"

"We did that already," Nico says, ignoring the sarcasm in my question. "Not me, not the New England group. Another team, in the Midwest, they already found him and secured his release. And now Jordan and I and the other New Englanders, we're just waiting to recon with the team."

I mouth the words disbelievingly. Recon with the team. All this B-movie dialogue. How many times, over the course of our lives, have I seen Nico's beautiful quicksilver brilliance dimmed: by grief, by alcohol and marijuana, by association with foolish minds.

"How can you believe any of this, Nico?"

"Because it's true," she says. She reaches into the warm refrigerator and pops the top on a mango soda. Summer rain taps against the glass and on the pavement outside.

"But how do you know that it's true?

"Because it is."

"That doesn't work," I say. "That formulation. You sound like Jesus Man."

"No, I don't."

"You do."

Jesus Man was the bright-eyed codger in the next bed over from Grandfather, in his last month or two, the final round of radiation before they gave up on Nathanael Palace and we took him home to die. Jesus Man had the light of the Lord, and there was no pain or discomfort that he couldn't bear smilingly through God's grace. He was practically celebrating it all, welcoming every new misery as a step on the road to paradise. Grandfather hated him-almost, he told me once, whispering loud enough for the other man to hear, as much as he hated the cancer itself. Once Jesus Man told Nico and me, while Grandfather slept, that he hoped we had accepted the Lord in our hearts. I didn't say anything when he said that, just nodded politely and looked at the TV. Nico, age seventeen, smiled and said, "Thanks, mister. I'll think it over."

Now she shrugs, stands up. "That's the whole story, big brother. I can't make you believe if you don't."

"Nope," I say. "You can't. When are you leaving? To recon with the team?"

"Soon. Jordan says they're on the way now. Tomorrow or the next day, a helicopter is going to land in Butler Field to scoop us up."

"Nico, I love you," is what I say next, and I'm surprised to hear the words coming out of my mouth; she looks pretty surprised, too. She crosses her arms, and I press on. "I do. And I made you a promise."

"I release you from that promise," she says immediately.

"You can't."

"We were kids."

"You were a kid," I say quietly. "I was fifteen. I knew what I was saying."

"I release you."

"No," I say, suddenly regretting my tone, my skepticism, regretting everything about the conversation. Don't go, I want to say, don't do it, just stay, come with me to Maine, come with me to Concord, Nico, don't go. Houdini is done eating and has found a place to lie down. In the silence, his snoring fills the room.

"Good luck with your case," says my sister.

"Good luck," I say, the start of a sentence, but I can't think of anything to finish it. That's all I've got. "Good luck."

Another scene from childhood. A few years after that spring, a few years before Jesus Man. Nico was nine years old and already she was sliding in and out of situations: insulting teachers, shoplifting small items. Stickers, cans of soda. A girl gave her beer, an older girl, probably as a joke, but Nico drank it all and was drunk-ten years old and drunk, and in her still-forming brain the alcohol was acting not as a goad to more bad behavior but as a truth serum, and she was muttering and sputtering, processing all kinds of anger toward me, toward Grandfather, toward everyone. "You will, though," she said, when I tried to hug her, lift her, carry her home. "You will go away like they did. You'll die. You'll disappear."

"I won't," I said to her. I said, "Nico, I will not do that."

The rain has exhausted itself, for now, and the sky is clear and untroubled, the stars twinkling in their familiar places. I try to sleep but can't; I can barely keep my eyes closed, lying restless on the floor of the India Garden, sprawled out uncomfortably with my backpack for a pillow. At dawn I will get back on the bike, get Houdini situated among my emergency supplies and water bottles, and leave for southern Maine.

Willfully I focus my thinking, put Nico and her friends and their tactics on a shelf in the back somewhere, pull a blanket down over Grandfather, who for some reason has been traveling with me all day today, emaciated and furious in his hospital bed with death crouching at his shoulders. I turn my head from everything and zero in on my case, my trip, my tomorrow.

So why are you doing it? Julia asked, as Nico had asked, as McGully had demanded of me. There are undoubtedly other ways I could be spending my time, performing actions of more tangible value to myself or others. But an investigation like this has its own force-it pulls you forward, and at a certain point it's no longer profitable to question your reasons for being pulled. I stay up for a long time, blinking into the darkness of India Garden, thinking about Brett Cavatone.

He'll ask me, too, if I find him, out there in the woods with his rifles. What are you doing here? Why have you come? And I don't know what I'll say, I really don't.

Route 4 meanders eastward from Durham and then north-northeast along the line of the Piscataqua River, offering me a wide rolling view of Portsmouth Harbor: rusting lobster traps bobbing unattended; boats listing in their abandonment, paint peeling, hulls jutting out of the shallows.

It's just me this time, bright and early and out on my mission. Detective Palace, retired, on his ten-speed with the dog hitched to the back in the little red wagon.

Cutts Neck-Raynes Neck-the long span of Memorial Bridge reaching high over the harbor. Then the series of roundabouts that spit you out onto 103 East. I know this route by pure sense memory from our handful of summers at York Beach, before the bottom fell out of my childhood. I roll past the big blue donut that had marked Louie's Roadside Diner, now torn from its mooring by weather or vandals and lolling across the parking lot like a giant's abandoned toy.

The sun is almost all the way up now, it's close to nine, and I'm leaning into the curve of the third roundabout, navigating around the pits and gashes in the asphalt, speeding past the gates of Portsmouth Naval Station on the seaward side. I'm coming. The woods huddle in close against the road as 103 crosses the border and cuts into southeastern Maine, gives up its last pretense of being a highway and settles down into a crooked little two-lane road with a faded yellow line down the middle.

Here I come.

Fort Riley, when I find it, sits on the northern lip of Portsmouth Harbor, a castle keep built on a cliff wall, staring out at the sea. For a couple hundred years it was an active United States Army fort, minding the coast during the Revolution, the War of 1812, all the way up to World War II, when civil reserves in green helmets would sit in seaside redoubts like this one, up and down the coast, peering out at the northern Atlantic for U-boats. For half a century Riley was a state park and historical site; now it's where Brett Cavatone, my missing man, has come to make camp. I turn off the highway into the parking lot, a long narrow spit of gravel with dense woods to the left and, to the right, the high tumbling stone wall of the old fort itself.

I get off the bike and lift Houdini from the wagon and set him down in the gravel. My chest is thick with anticipation. The air smells like the sea. He's here, I'm thinking. This is it. Hello, sir. My name is Henry Palace.

I walk slowly down the length of the parking lot, hands out of my pockets and slightly raised, a picture of harmlessness, in case anyone is watching-anyone with a pair of sniper rifles and reason to be wary of visitors. There's one car in the lot, a gray Buick LeSabre with Quebec plates and all four tires shot out. In the backseat, a teddy bear and an Uno deck. The entrance to the fort is all the way at the end of the parking lot, an arched doorway just where the stone wall bends away to the south and the gravel ends in grass and weeds. Farther on is the ocean.

Put down your weapons, sir. Your wife would like you to come home.

"Okay," I say, to no one, or to the dog I guess, but then I see that he's decided to stay back by the bicycle. I turn around and he's way back up there where the parking lot begins, skittering back and forth between the chained-up ten-speed and our supply wagon. I gesture to my right, around the corner of the wall, into the fort proper.

"You coming?"

Houdini doesn't answer. He growls uneasily, sniffs at the ground. "All right," I tell him. "You stay there."

The buildings of the fort, half a dozen tottering stone piles and decomposing wooden ruins, are scattered over one big uneven hill-an acre or acre and a half of muddy grassland, sloping down toward a cliff over the water. The layout is as haphazard as might be expected of a centuries-old military campus, built piecemeal by different commanders at different times for different purposes. It's all centered around one structure, though: the blockhouse, a wooden tower on a sturdy granite base, rising high above the center of the fortland like a birthday cake. The blockhouse could be somebody's tidy colonial house, a charming white-sided vacation home overlooking scenic Portsmouth Harbor, except that it's perfectly octagonal and slitted all around its eastern faces with narrow rifle ports, for spotting incoming ships and shooting at them.

I shade my eyes and look up at the narrow windows. He might be up there. He might be in any of these buildings. Cautiously I pick my way through the mud and seagrass, over the foundation stones like flat gravestones, alert for the presence of Brett.

The rifleman's house is a square red-brick building, as small as a one-room schoolhouse. A cornerstone announces the structure's provenance of 1834, but there is no roof; maybe it was never completed, or maybe the tiles were repurposed by the army when this fort was decommissioned, or maybe they were stripped last month by looters and carted away like Sergeant Thunder's brick shed.

I linger there in the roofless shelter. This then will be the shape and the feel of the world: an abandoned shell, signs of old life, curious animals wandering in and out of ruins, the wilderness crowding in, overtaking all human structures and human things. In fifty years, everything will look this way, desolate and quiet and overgrown. Not even fifty years-next year-by the end of this one.

I make my way carefully down the gentle slope to the granite wall that rings the fort's easternmost edge. There's a narrow trench dug into the mud just in front of the wall, except it's not a trench at all, it's an entrance, a stairhead carved out of the wet ground. A gash in the base of the wall, and then a short steep staircase into a dark chamber with a wet clay floor. The room is dank and close, as long and narrow as the barrel of a gun. A brass plate screwed into the granite wall identifies the room with an unfamiliar word: caponier. It smells like brine and fish and ancient mud. Light seeps in through nine high slit windows along the eastern face.

I am too tall, in a room like this. It bears down on me, coffin-like, and I can hear my heart beating, experience an unexpected sharp awareness of my body's functioning as a machine.

I walk slowly across the room and lean into one of those slitted windows and squint. To the south there's a lighthouse, to the north, uninterrupted miles of Maine coast. Way out on the horizon is the tiny black dot of an incoming ship and, twenty degrees to its left along the blue-green horizon, the tiny black dot of another. I stare for a minute, watching them come.

They must come all day. Big ships, their holds packed with desperate cargo, famished and exhausted, people from all over the world, the Eastern Hemisphere emptying itself out.

As I watch I see a third one, another speck on the far edge of the horizon, almost to the lighthouse on the harbor's southern lip. I have a sudden vivid picture of the earth as flat, a tray, covered in marbles, and someone is tilting it, and the marbles are rolling, cascading, from east to west.

"It is hard to imagine the conditions onboard those ships."

A voice deep and calm, and then there's the scrape of a boot heel behind me, and I take a breath and turn around and there he is at last.

"The countries of origin, many of them, were impoverished to begin with," says Brett Cavatone, his voice soft, even, scholarly. "More so since Maia. The ships are packed with travelers. They live in darkness, below decks in miserable dank holds, crawling with rats and bugs." His beard has grown in more, thickened into a dense black jungle. His eyes are deep set and black as a well. "It is hard to conceive of what they eat, on those ships, or how they drink. Still they come."

"Officer Cavatone, my name is Henry Palace. I'm from Concord." He doesn't respond. I keep talking. "Martha asked me to find you. She wants you to come home."

Brett's face betrays no surprise or confusion at this announcement. He doesn't ask, as I have anticipated, how I found him or why. He just nods his head, once-message received.

"And has Martha found Mr. Cortez?"

"Yes."

He nods again. "And is Mr. Cortez honoring our bargain?"

"Yes," I say. "I think so."

"Good. Then Martha is safe? And healthy?"

"She's devastated. Heartbroken."

"She is safe and healthy?"

"Yes."

Brett nods a third time, nods deeply and closes his eyes, almost bows. "Thank you for coming."

I hold up my hands. "Wait. Wait."

It doesn't seem fair. It doesn't seem real, somehow, that at the end of this journey I should find a thirty-second conversation, a quick fair hearing and then goodbye, thank you for coming.

"Do you have a message for me to bring back to her?"

Brett closes his eyes and steeples his fingers. He's in camouflage pants but a plain white T-shirt, sandals on his feet. "You may tell her that the asteroid has forced some hard decisions in me, as it has in many of us. Martha will understand what I mean."

"No." I shake my head.

"No?"

"Respectfully, sir, the asteroid did not make you leave her. The asteroid is not making anyone do anything. It's just a big piece of rock floating through space. Anything anyone does remains their own decision."

A smile flits across his lips, down in the thickness of facial hair. "You asked me to provide a message, and now you disapprove of it?" His voice is deep, hushed, rhythmic, like an Old Testament prophet. "You have discharged your obligation, friend. Your work is done, and now I must return to my own."

"You are a married man," I say. I'm pressing my luck. He stares back at me in silence, impassive as a mountainside. "Your wife is confused. You've left her terrified and alone. You can't just abandon your promises because the world is over."

I'm aware, even as I am talking, that these arguments are doomed to be unavailing. It is clear that Brett Cavatone is as rooted in his purpose as the fort's stone walls, planted for centuries in this craggy soil, and my suggestion that he return to Martha and Rocky's Rock 'n' Bowl is not only impossible but ridiculous, juvenile somehow. Oh, why should he do what I say? Why, again? Because he promised?

"I am not coming home." He looks steadily at me, black eyes under furrowed brows. "Tell her that. Tell her our contract has been abrogated. She will understand."

I can see her, Martha Milano at her kitchen table, aghast with grief, hand trembling on her teacup, stalking back and forth to the cigarettes she will not allow herself. "No," I say to Brett. "I don't think she will understand."

"You said your name was Henry?"

"Henry Palace. I used to be a policeman. Like you."

"There are things you don't understand, Officer Palace. Things you cannot understand."

He takes a step toward me, compact and powerful as a tank, and my mind flies to the little gun tucked in the inside pocket of my blazer. But I have no doubt that Brett, if he wanted to, could be on top of me before I drew, hammering me with his fists. Condensation drips from the ceiling of the room, sweats down the walls. I have to say one more thing, though. I have to try.

"Martha says your salvation depends on it."

He repeats the single word, "salvation," lets it hang in the gloomy air between us for a moment and then says, "I'll need you to leave the grounds of this fort within ten minutes."

He turns on the steps, presenting me with his broad back, and takes the first step out of the darkness of the caponier.

"Brett? Officer Cavatone?"

He stops, speaks quietly over his shoulder, without turning around. "Yes, Henry?"

I pause, gut rolling. Seconds pass. Yes, Henry?

My investigation is over. Case closed. But I hear Julia's voice in my head, tense and taut with anxiety: Danger? I mean, danger doesn't even ...

I find that I cannot leave. I don't know anything, but I know too much to leave. Brett is still waiting. Yes, Henry?

"I know what you're doing," I say. "I met Julia Stone, and she told me. She explained your intentions."

"Oh," he says calmly. "Well." He is incapable of being surprised.

"And I-I'd like to help."