She's not alone in the room, though. A big, bearded man is kneeling on a prayer rug between the bed and the door. Luckily, there was some information about this guy in the Sigma memory files that I saw just a second ago. He's a Chechen terrorist named Imran Daudov, one of a half-dozen fanatics whom Sigma hired to smuggle the batch of anthrax into Tatishchevo. Afterward, the AI decided it didn't need so many human collaborators, so it ordered Imran to murder his fellow terrorists. The guy obeys Sigma without question because he thinks the AI is God. He actually believes he's hearing the voice of the Lord when Sigma talks to him from the lab's speakers. I guess terrorists aren't the most stable people in the world.

I hate to play the same trick on him that Sigma did, but I don't have a choice. I download an English-Chechen translation program from the lab's database, then connect to the speakers on the nightstand beside the bed.

"Imran! I have new orders for you!"

The guy jumps up from his prayer rug. "Yes, my Lord!"

"You must free the girl. Then run away from this building and surrender to the soldiers outside the missile base."

"My Lord, I don't understand-"

"Silence! Just do as I say!"

Imran bows low, clasping his hands together. Then he approaches the bed and unties the straps. Meanwhile, Brittany keeps on sleeping. This doesn't surprise me. Ever since she was a little kid she was famous for being a heavy sleeper. After Imran undoes the last strap, he rolls up his prayer rug and bolts out of the room. Sigma's servant is obedient to the end.

Half a second later, a loud thud makes the walls shiver. I've heard this noise before-it's a T-90 shell exploding somewhere near the computer lab. I don't know who fired it, one of Sigma's tanks or one of ours, but the odds are good that another shell will hit the building pretty soon. I need to get Brittany out of here before that happens.

"Brittany!"

Her eyes open at once. "Adam?"

There's no time for long explanations. In a hundredth of a second I come up with a decent lie. "I'm in another part of the building. I'm talking to you over the intercom."

Confused, she stares at the speakers on the nightstand. Then she notices that she's no longer tied to the mattress. She sits upright in bed. "What happened? Where's the jerk with the beard?"

"The place is under attack, so everyone left. And now you have to leave too."

"Wait, where are you? I don't know which way to go."

"Okay, it's easy. Once you leave the room, you'll see the stairway. Go upstairs to the lobby, then straight out the front door. Then get as far away from here as you can."

Another thud shakes the room. Brittany slides out of bed and takes a few wobbly steps. Then she stops. "Adam, I'm scared! Why can't you come help me?"

Her voice is heartbreaking. But there's nothing else I can do for her. "Don't worry, Britt, you'll be all right. After you leave the building, keep going till you find some soldiers. Tell them to take you to General Calvin Hawke. Can you remember that name?"

She nods, then looks at the speakers again. "Will I see you there? Will you be with this Hawke guy?"

"Definitely. Now go, okay?"

Brittany nods again and goes out the door.

I keep looking at the empty room after she leaves. I have two reasons for feeling nervous. First and foremost, I'm worried about Brittany's safety. I'm praying she gets out of the lab before it goes up in smoke. But I'm also worried about what'll happen afterward. I don't know how Brittany will react when she sees what I've become.

Then I get a message from Marshall.

Adam, we have a problem!

What is it? Did you shut down the dish antennas?

I was about to disable the last one when Sigma escaped from Zia and occupied the antenna's circuits. The AI transmitted its data before I could stop it.

Where did it go? To one of the communications satellites?

No, this antenna wasn't pointed at a satellite. Sigma modified the device so it could be used for wireless communications between the computer lab and the nuclear-missile silos.

Sigma's in one of the silos?

No, it's in the missile itself. And it just launched.

SHANNON'S LOG APRIL 8, 04:43 MOSCOW TIME.

"Shannon? Are you in that tank in front of the lab?"

It's Adam. He's using a dish antenna on top of the computer lab to contact my T-90. Over the radio his voice sounds thin and strained, but it's definitely him. My circuits hum with joy.

"I knew it! I knew we'd find you! I'm so-"

"Shannon, there's no time. Sigma just launched one of the nukes."

"What?"

"Look to the northeast. That's where the silo is."

I turn my T-90's camera in that direction. A thick plume of flame is rising above the fields and woods. Within seconds it grows as bright as dawn, illuminating half the sky. On top of the plume is a tall dark column, its edges outlined in fire. That's the SS-27 nuclear missile. It ascends slowly at first, fighting gravity, but soon it's streaking upward.

My joy vanishes. My circuits fall silent. The missile's ascent is nearly vertical, but after a few seconds it tilts to the north, following a trajectory that'll carry the nuke over the Arctic Ocean. Somewhere in North America, millions of people have less than half an hour to live.

Adam's voice cuts through the silence. He's sending radio signals as fast as he can, trying to cram a whole conversation into a hundredth of a second.

"Tell me about the interceptors, Shannon. The rockets that can hit a nuke in midflight. I saw two of them at the military airfield where your C-17 landed."

"How did you see them? You weren't there."

"I saw them in Jenny's memories. The rockets were on mobile launchers. They looked like they were ready to go."

I want to ask him what happened to Jenny, but I don't. Something in Adam's voice is telling me that I won't like the answer. Instead, I concentrate on my own memories of the interceptors. "Hawke said they were upgrading the rockets because their electronics were vulnerable to Sigma's computer virus."

"Upgrading? What do you mean?"

"He wasn't specific. His soldiers were carrying boxes of equipment from the C-17 to the launchers."

"Check your memories. What was in the boxes?"

I reach into my files and retrieve an image of the airfield. I see the C-17 with its cargo door open and Hawke's soldiers unloading the plane. And I see the boxes in the soldiers' hands, the equipment they brought all the way from Pioneer Base.

"They were neuromorphic control units," I report. "Hawke said their circuits can't be infected by the virus. That's why the soldiers put them in the interceptors."

"Bingo. I'm going to the airfield."

"Wait, Adam, what do you-"

He breaks off radio contact. I turn my T-90's camera toward the dish antennas on the roof of the computer lab and see one of them pivoting. Adam's pointing it east, toward the military airfield. He's going to transmit his data to the control units in the interceptors.

Thirty seconds later Adam launches the rockets. Two more fiery plumes rise above the eastern horizon.

CHAPTER.

23.

I feel like I'm walking on a pair of stilts. Except each of these stilts is fifty feet high and shooting upward with 200,000 pounds of thrust.

I'm occupying both of the interceptors, which are ascending from the Russian military airfield. Using their powerful radios, I send streams of data from one control unit to the other, keeping me balanced between the two rockets. Each interceptor also has an amazing camera, designed to detect objects that are hundreds of miles away. I point my cameras upward and focus them on the brilliant plume trailing Sigma's nuclear missile. It launched nearly a minute before I did, and it's already twenty miles above me.

To stop the missile, I need to slam into it while it's still ascending. If I can hit it with one of my interceptors while it's still rising, the impact will pulverize the nuke before it can explode. But once the SS-27 reaches an altitude of one hundred fifty miles, its rocket engines will shut off and the missile will release its nuclear warhead, which will coast the rest of the way to the target. At the same time, the SS-27 will release a dozen decoys that look identical to the nuke. So I have to hit the missile before it gets to that point, which will occur in three minutes. If I don't, the warhead will slip past me, and I can tell from the missile's path where the nuke's going to land.

It's heading for New York.

My only hope is speed. The interceptors can reach a maximum velocity of 20,000 miles per hour, while the SS-27 tops out at 15,000. It's possible, of course, that Sigma modified the missile to make it faster, but I can't worry about that right now. All I can do is push my rockets to the limit and try to catch up.

Each interceptor has three rocket stages, and now my first-stage engines are firing like crazy, trying to overcome gravity and the air resistance of the lower atmosphere. I feel slow and ungainly, like I'm moving through mud. Instead of catching up to Sigma's nuke, I'm falling behind.

But then, after another minute, I start to accelerate. Once I'm twenty miles above the ground, the air gets thinner and there's less resistance. Then the bulky first stages detach from the bottom of my interceptors and the second-stage engines come roaring to life.

Now I'm smaller and lighter and full of power, and I start climbing into the upper stratosphere. My rockets tilt to a forty-five-degree angle as I chase Sigma's missile, which is arcing northwest over the Russian countryside. I'm still far behind, but I'm getting closer.

Then I get a radio message. From the SS-27.

"You won't intercept me. You're going to fall short."

I've already modified the interceptors' radios to prevent Sigma from transmitting its data to my control units. The AI can only send short messages to me. I'm not at its mercy anymore.

"We'll see about that," I radio back.

"It isn't a matter of opinion. I've analyzed the paths of your interceptors. My calculations show that you'll fail to reach me in time."

"Sorry, I don't trust your predictions. You've been wrong a little too often."

"That's incorrect. My calculations have always been accurate."

"Really? So you predicted that I'd escape from the isolation cage? And that Zia would kick your butt?"

"I never made predictions about the Pioneers. I didn't have enough information about your capabilities."

"Well, you lost. We beat you. And what you're doing right now is just stupid. You're upset because we messed up your plans, so you're going to blow up New York City. You call that intelligent?"

Sigma falls silent. I guess the truth hurts.

After a few more seconds I reach an altitude of sixty miles. The second stages detach from my interceptors, and my third-stage engines fire up. Then I really start to fly. I'm in the thinnest, uppermost part of the atmosphere. Soon I'm high enough that I can see the curving edge of the planet. The Russian cities are twinkling like stars below me, and to the east I see the glow of dawn over Central Asia. But I keep my cameras trained on Sigma's missile. I'm catching up fast.

Then I hear its voice again. "I haven't lost. This was merely the first phase of the competition. I plan to analyze the performance of the Pioneers. Then the second phase will begin."

"Not if I hit your missile first. You should double-check your arithmetic."

"I've already made the necessary arrangements for the second phase. If you point your cameras toward the zenith, you'll see what I mean."

I look in that direction-straight up-and see a gleam of reflected light in the middle of the familiar constellations. It's a satellite, one of Sigma's communications satellites. It's orbiting the earth about two hundred miles farther up.

"Oh, I see. You're gonna transfer out of the missile and run away. You're afraid of us."

"No, not afraid. But I've learned enough to be cautious."

"You better hope Zia doesn't find you."

"I'm not concerned about her. You're the dangerous one, Adam Armstrong."

"What?"

"You're the most dangerous Pioneer by far. You don't even realize it, do you?"

This confuses me. I have no idea what Sigma's talking about. But it doesn't matter. My interceptors are streaking a hundred miles above the earth, both closing in on Sigma's missile. I let one of my rockets move in front of the other. If the first rocket misses the SS-27, I'll hit it with the second. Either way, one of my interceptors will survive. Then I'll steer the remaining rocket back to Saratov and transfer my data to a control unit on the ground.

There's only ten seconds left until impact. The AI starts transferring itself to the satellite. My instruments detect the huge transmission of data.

"Good-bye, Adam Armstrong. Try to save New York if you can."

"Don't worry, I'll save it. It won't even be close."

Then Sigma is gone. The AI escapes into the satellite network, leaving the speeding missile behind.

Only five seconds left now. I'm closing in at a rate of a mile per second. Like I said, it won't be close. I'm going to smash into the missile a full minute before it releases its warhead.

And this bothers me. How could Sigma get its numbers so wrong? It seems unlikely that the AI would make such a big error.

So maybe it wasn't an error. Maybe Sigma was lying when it said I'd fall short.

But why would the AI lie? What did it hope to gain? The practical effect of the lie was that it made me more desperate to intercept the nuke. I pulled out all the stops and flew even faster toward the missile.

Then I figure out the answer: Sigma wants me to catch up. It wants me to reach the missile before it releases its warhead Oh no.