Jack closed the door leading into Gary's fortress and got to work by the illumination of a handful of chemical lights. We took off our hazmat suits to make it easier to work and I waited patiently for Jack's instructions. He unzipped the big pack I had carried into Gary's fortress and took out a couple foil packets covered in warning stickers and small print type. I peered into the pack myself and had no idea what I was looking at. Other than the metal gas cylinders there were neat stacks of electronic components and bricks of something soft-looking and off-white. I did notice what was missing: guns. There weren't any firearms in there at all. No pistols, no assault rifles, no shotguns. No rocket launchers or sniper rifles or machine guns.

No knives, either. The combat knife strapped to my suit's leg was the only weapon I could find. I unzipped Jack's pack, thinking maybe he had carried all the armaments because he didn't trust me not to accidentally shoot off my foot (a fair enough assertion, if that was what he had actually been thinking. It wasn't). He reached over and stopped my hand. "I'll unload that," he said.

"Are you ready to tell me what we're doing?" I asked, cautiously.

"No," he said.

Pure Jack style. Just no, negative, unh-uh. He took the Iridium cell phone out of my pack and laid it on the floor after checking for probably the third time that it was set to vibrate and not to ring. "One at a time, and very slowly, start handing me those bricks," he said, pointing to my pack.

I took one out. It felt slightly powdery, like a crumbling bar of soap and it came wrapped in a thin sheet of plastic, like Saran wrap. I left a depression in the brick where I held it with my thumb but Jack didn't seem to mind. He stripped off the plastic and then picked up one of the compressed gas cylinders and wrapped the putty-like substance around the cylinder, smoothing it quite carefully. As he worked with it the stuff lost its powdery consistency and became rubbery and malleable.

I had seen the stuff before. It's common enough and cheap enough that it regularly shows up in the arsenals of most developing countries. Not to mention terrorist training camps. "That's semtex, right?"

Jack glared at me.

Foolish me, I thought he was angry because I had used a European name for it. "Sorry. C-4. Plastic explosive. You're going to blow Gary up."

"Something like that." He returned to his work, fashioning a charge around the end of a second cylinder.

I had to know. I picked up one of the cylinders. It had a faded sticker near the nozzle showing two symbols. One was a triangle containing a broken test tube. Cartoon fumes rose from the point of breakage. The other symbol was a skull and crossbones.

The foil packets contained two piece atropine auto-injectors. First aid in the event of a chemical weapons spill. "What is it in those cylinders, sarin?" I asked, very, very calmly.

"VX," he said, with something of a sniff. As if I had offended his professional pride. "It's got an LD50 of ten milligrams, either inhaled or cutaneous."

A lethal dose of one thirty thousandth of an ounce. One little droplet is all it takes. I knew a hell of a lot more about LD50s and cutaneous versus ocular exposure rates than I had ever wanted to. This stuff was my worst nightmare back when I was working as a weapons inspector. It would have been everybody's worst nightmare if anybody had ever been crazy enough to use it. Even Saddam Hussein, when he tried to wipe out the Kurds, had used less dangerous nerve agents than VX. The British invented it. They traded it to the US in exchange for the plans for the atomic bomb. It was that lethal.

"The military tried everything they had when the Epidemic broke out," Jack told me. "There was a rumor they were going to nuke Manhattan but I guess they couldn't make it happen in time. They did try gassing Spanish Harlem. This is all that's left of the assets they brought down for that project."

"They used nerve gas against the living dead?" I asked, incredulous. I suppose if I was put in the same position I might have grasped at straws, too. "Did it... did it work?"

"It should have. A dead guy is pretty much just a nervous system that can walk around and VX is a nerve agent. It short-circuits the acetylcholine cycle. It should have worked."

Obviously it hadn't. If anything the military had probably wiped out any survivors holed up in the neighborhood while leaving the undead untouched. The things we do with the best of intentions... I shook my head. "Then you aren't here to kill Gary at all."

Jack reached into his own pack and pulled out a handgun, a Glock 9mm. He didn't point it at me, didn't threaten me at all. Very carefully, the barrel pointing at the wall the whole time, he placed it on the floor.

"I told you one time about my contingency plan. About how I used to think about killing them in their sleep." He continued to build the charges around the cylinders. I did nothing. I remembered quite well what he had said. It had scared me then - it scared me more now because now I knew he meant it. He went on. "There's no hope for a rescue attempt, Dekalb. It just can't be done. I ran through a million scenarios in my head and there's no way the two of us come out alive."

"You don't know that," I demanded.

He blinked and looked away from me. "Dekalb," he said, "what's the crew carrying capacity of a Chinook helicopter with the seats taken out?"

My jaw opened and closed spasmodically. "You don't - " But he did. He knew the answer. Maybe a hundred people if you're not going very far. We could only rescue half the survivors, even if we made it that far.

Jack clearly didn't want to have to choose which ones to leave behind.

"There's nothing to be gained by us dying like that. Still we can do something for the survivors. We can keep them from being his lunch. Or rather I can."

He tossed me one of the atropine injector kits. If I was exposed to nerve gas the only thing that could save me - the only thing - was jabbing the enclosed hypodermics into my buttocks or thigh. If I hadn't been exposed to nerve gas but jabbed myself anyway, the atropine would kill me instead.

"You can get out of here. Go back the way we came. Meet up with Kreutzer and have him take you to the UN. Get the girls off of that rooftop. You can still complete your mission. You just have to let me complete mine."

Which meant consigning two hundred men, women and children to their deaths.

"Dekalb - I only needed you to come this far because I couldn't carry all of this gear on my own. Now let me do you a favor. Just turn around and go."

I didn't know what to say. I definitely didn't know what to do. I most certainly had no idea what my next reaction was going to be. If I could have stepped out of my body and spoken with myself I would have advised against it.

It was a kind of spur-of-the-moment thing.

The Iridium cellphone buzzed with a small, unobtrusive sound. It vibrated against the flagstone stone floor, wobbling and dancing. It slid a few inches across the floor and stopped. It started up again a second later. This was Ayaan's signal to us, the message that she had drawn Gary's undead army to her position. Away from us. Jack and I both stared at the phone.

We looked up at the same moment. I had my combat knife in my hand, pointed at his stomach. He had the Glock in his hand, pointed at my heart.

I lunged.

He fired.