We followed Jack's flashlight up a never-ending series of stairs and stalled escalators. It got easier to see as we went along. I thought my eyes were adjusting to the darkness but in fact we had merely arrived at Grand Central and light - real sunlight - was streaming through the terminal's high windows. When we emerged into the marble-lined corridors leading to the main concourse I could suddenly see everything again and I blinked rapidly, my eyes watering.

Ayaan dropped into a crouch and scanned the empty terminal from behind her rifle. Jack kept close to the walls but I was just so glad to be out of the tunnels that I couldn't maintain that level of healthy paranoia. I lead them past empty newsstands, empty shops selling men's shirts or CDs or flowers, past a deserted shoeshine stand until we entered the big main concourse and I could look up at the green-blue ceiling and the gold diagrams of the Zodiac, at the enormous windows through which streamed visible rays of yellow light. There was no sign of any life or movement anywhere.

The emptiness of Times Square had shocked me and this should have, too. Grand Central had never been anything but crowded in my experience. Yet something about the place - its cathedral scale or its gleaming marble, perhaps - lent itself to a kind of somber peace. I didn't have time to sight-see, really, but it was hard to tear myself away from the massive quietude of the terminal. This was a place built for sleeping giants and I longed to rest a while in its megalithic grace.

I lead them down the Graybar Passage to a row of glass doors. They were locked at the top and bottom but Jack had a police pick gun. It looked like a pistol grip with a thick needle sticking out where the barrel should have been. It could open any lock in the city. It used to be that only civil authorities could have such things but the internet had made them publicly available - Jack had got his from the same outfit that sold him the SPAS-12. "Check the street," he said, as he crouched down to get at the bottom lock on the door. It was a tricky operation - you had to fire the gun to retract the cylinder pins at the same time you used a tension wrench to turn the plug.

I peered out through the glass at Lexington Avenue and saw abandoned cars and dead buildings but nothing animate anywhere, just a flock of pigeons wheeling between the glass walls of a pair of deserted office towers. It looked like our luck was going to hold. From here it was just a few short blocks to the UN building. If we were quiet and didn't draw any attention to ourselves we just might make it. It was almost as if something had cleared out this whole section of the city. Perhaps the National Guard had put up barricades to keep the dead out. Maybe they were even still there, living soldiers protecting this last bastion of New York.

"Anything?" Jack asked. The lock released with a loud clang that startled the birds outside. They leapt into the air, their wings snapping out as they rode up into the sky, one after the other. Jack stood up and started working on the top lock.

"Negative," Ayaan said. She watched the birds, entranced as I was, perhaps observing how they relied totally on each other, each animal mirroring the movements of its neighbor so that each time the flock changed its position a wave of motion seemed to go through them, as if they were a single entity with many bodies.

The second lock shot open and Jack put his tools away. He pushed on the door's latch bar and it swung open, letting in a cool puff of air from outside.

Air that stank of decay and rot.

"Get down!" Jack shouted as the flock of pigeons swung through the air, pivoting to dive headlong through the open door. The ex-Ranger slammed the door shut as dozens more of the birds smacked up against the glass, their filmy eyes showing nothing but naked desire. Hunger. One of them lay twitching just inches from my face, separated from me by only a thin piece of safety glass and I saw the marks on its spine where it had been pecked to death, disarranging its iridescent feathers. Its beak snapped at me against the glass door, desperate for a bite of my flesh.

I heard wings flapping behind me and Jack rolled up into a sitting posture, his shotgun in his hands. He fired and the noise echoed wildly off the marble walls. Birds fell out of the air right and left as those pigeons that had made it inside doubled back for another go at us. He fired again, and again, and Ayaan opened up with a volley of fully automatic fire that blew the undead birds into clouds of blue feathers and wet gore. My ears ached with the noise and I worried they might start bleeding.

I felt pressure on my back and looked to see pigeons colliding with the door behind me, trying to bludgeon it open with their bodies. I put my shoulder against the door while Jack finished off the last of the intruders, stepping on the heads of the ones his shots had only crippled. Ayaan put her rifle over her shoulder and helped me as the birds outside redoubled their efforts.

"This is crazy!" she said. "Fucked up!"

Jack hurriedly re-locked the door with shaking hands. The attack had surprised even him. "Undead animals... you don't see a lot of them. Most of the city's wildlife got eaten in the first couple of weeks. I can't remember the last time I saw a squirrel."

"What do we do?" I asked, stepping away from the door as another pigeon smashed itself against the barrier. The glass was cloudy with the grease of their bodies. "This is ridiculous. What do we do?"

Jack shook his head. "So close. If we abort now - "

"No one is aborting this mission," Ayaan said, scowling at us. "I have lost my commander to get here. I have lost my friends. Now is not the time to stop. There will be a way, if we look."

In defiance of her words a shadow passed across the sidewalk outside. I looked up and saw a new flock of birds approaching. It was almost as if they were organized, as if they could plan their attacks. It was just instinct, though, something in the bones that they didn't even need their tiny brains for. Pigeons were social animals, taking their cues from one another just as they always had. I could imagine how they had come to own this part of the city. One of them must have been bitten by a dead human looking for a quick meal. It had escaped but died of its injuries. Returning to its flock it would have attacked its fellows - who would attack the ones next to them, who would turn to do the same. The flock that flies together dies together, I suppose. The Epidemic must have spread through the avian population of New York even faster than it had through the humans.

I wondered for a moment what they were all doing here, so close to the East River. Then I understood and my blood went cold. Hungry things went where the food was. The dead humans had eaten pretty much everything on the land. The last big source of food was clogging the river as far south as the Brooklyn Bridge. I'd seen it from the deck of the Arawelo.

There had been hundreds of thousands of pigeons in the city before the Epidemic - now they had joined forces, an instinct stronger than death. "If we go out there," I said, "we'll be pecked to death in seconds." It sounded hilarious but nobody laughed. "There are tunnels around here, though. There's one that leads to the Chrysler Building, I know that. If we came out of the ground somewhere else, somewhere they weren't expecting."

Jack nodded. "Sure. And if the wind is just right they won't smell us. And if we take off our shoes we can walk silently. Sure. We'd make it one or two blocks before something changed and they realized where we were."

I stared out through the doors, looked between the buildings. I couldn't see the Secretariat Building of the UN from here, not quite. But I could almost feel it, no more than ten minutes away by foot. We were so close.

Fate made up our minds for us. The Iridium cell phone in my back pocket rang, a strident pulsing chime that annoyed me so much I grabbed at it and answered the call. "Dekalb here," I said.

I expected to hear Marisol's voice but it was a man who answered me. "No shit? Dekalb? I just found this phone and hit star sixty-nine. I must have just missed you. This is awesome! Is Ayaan there with you?"

"She is - who is this?" I asked. Osman? Shailesh? It didn't sound like either of them but I knew I recognized the voice. Then I had it and my back rippled with icy fear.

"Who am I? I'm the guy who just ate the President of Times Square."

"Hello, Gary," I said.

I hurriedly hit END as if he could come through the satellites and get at me. "Jack," I said, trying to sort it out, "there's a problem at the station. The dead - "

He didn't wait for me to finish the sentence. He turned on his heel and bolted back toward the subway entrance as fast as he could go. I called after him and Ayaan ran a few steps but then she turned and looked at me. Her face was a question I didn't want to answer.