Zia's voice suddenly comes over the radio. "Don't be an idiot, Armstrong! Get out of here!"

"Where are you? I don't see you anywhere."

"Watch it, the tank's about to fire! Get behind the ridgeline, now!"

Her warning comes too late. I'm still a hundred yards from the top of the ridge when the T-90 fires a shell straight at me. For a moment I'm frozen in terror. If the shell hits the helicopter, my Pioneer might survive the explosion and crash landing, but Dad definitely won't make it. Although he's still lying unconscious on the floor of the crew compartment, there's a grimace on his face now, as if he can somehow sense the fast-approaching projectile.

No! I won't let you die!

The fury in my circuits overcomes my fear. I roll the Black Hawk to the left, banking away from the shell. Fortunately, the projectile has no guidance system, so it can't adjust its course in midflight. The shell whizzes past the helicopter's tail and slams into the ridge, spraying snow and dirt into the air. Two seconds later I swoop over the ridgeline and dive for cover. I descend behind the ridge's north-facing slope, putting the mountain between me and the T-90.

"Now go!" Zia shouts over the radio. "Get out of here and call for help. That's an order, Armstrong!"

I'm not going anywhere. She should know by now that I'm not good at following orders. Instead I analyze her radio signal to figure out where she's hiding. As I suspected, she's crouched behind an outcrop on the south-facing slope, concealed so well she didn't show up on my infrared scans. But Sigma knows where she is. The T-90's shells have already gouged the outcrop, blasting holes in the wall of rock that's protecting Zia. I can't leave her behind. Sooner or later the tank will destroy her.

"Zia, I have an idea."

"I told you, Armstrong, get-"

"For once in your life, will you listen? Right now I'm in two machines, the Black Hawk and Pioneer 3A, but I'm going to take myself out of the robot so you can transfer to it."

"No, I can't transfer. You're too far away. And the ridge is between us."

Unbelievable. She's so stubborn she'd rather die than admit she's wrong. "Trust me, you can do it. Just wait for my signal, then start transmitting, okay?"

Before pulling out of Pioneer 3A, I bend over Dad and squeeze his shoulder. Then I begin to remove my data from the robot, consolidating all my files in the Black Hawk's control unit. Another shell from the T-90 explodes against the outcrop that Zia is hiding behind, but she shouts, "Don't worry, I'm okay!" over the radio. In just a few seconds Pioneer 3A will be vacant and she'll be able to transfer. This is going to work!

Then I hear another shout over the Black Hawk's radio, but it's not Zia. It's a signal from Globus-1, a Russian communications satellite that's 22,000 miles overhead. The signal originated from the other side of the world, then bounced off the satellite and returned to earth, but the voice I hear is achingly familiar. It's a voice from my past, its memory etched into my circuits and linked to thousands of other memories. It's so powerful that even a whisper would be enough to make me tremble. But Brittany is screaming.

"Adam! Adam!"

All my systems freeze. My wireless data transmissions stop in midair, leaving me suspended between Pioneer 3A and the Black Hawk. I'm so shocked and confused that I can barely keep the helicopter flying. "Brittany?"

"Oh, God, you have to help me! He's hurting me! He's-"

She lets out a horrible shriek of pain. At the same time, I feel a sudden jerk upward, but the Black Hawk isn't climbing. The movement I sense is inside my mind. I feel as if someone is trying to yank me out of both the helicopter and the Pioneer.

"Brittany? Brittany?"

The thing that's pulling me upward grows stronger. I try to hold on to Pioneer 3A and the Black Hawk, but an implacable force has invaded my electronics. It's prying my thoughts and memories from my circuits and transferring the data elsewhere. My files are shooting upward at the speed of light, streaking toward the communications satellite.

It's Sigma. The AI carefully prepared its attack, disrupting my thoughts before taking over my circuits. For the first time I sense the full strength of its intelligence. Sigma was designed for this kind of battle, programmed to win at all costs, and it defeated me without much trouble. Now I'm at its mercy. I've already lost control of the Pioneer, and my grip on the Black Hawk is weakening.

Terrified, I concentrate on protecting Dad. I slow the Black Hawk and hover over a snowbank on the north-facing slope. I don't have enough time to land the helicopter, but I turn on its emergency rescue beacon. I don't know if Dad will survive the crash. And if he does, I have no idea whether the rescuers will reach him before he dies of exposure. But there's nothing else I can do.

Then I lose contact with the helicopter and the Pioneer. My mind is funneled into a narrow beam of radio waves, which Sigma hurls above the atmosphere and into the emptiness of space.

SHANNON'S LOG APRIL 8, 01:41 MOSCOW TIME.

This isn't good. The city of Saratov is burning.

We're descending toward a Russian military airfield on the eastern side of the Volga River. The C-17 doesn't have any windows in its cargo hold, so I'm using my antenna to intercept the video from the plane's cameras, which give me a panoramic view of the landscape below. The fires are everywhere, lighting up the night sky on both sides of the Volga, but the biggest blaze is on the western edge of Saratov, the part of the city closest to Tatishchevo Missile Base.

It looks like Sigma started the war without us.

I take a closer look at the video. The Russian troops have pulled back from their positions next to Tatishchevo, abandoning the camps they set up around the missile base after Sigma took it over. The deserted camps are at the center of the biggest fire. The roads are dotted with hundreds of burning cars and trucks and tanks.

While I'm examining the destruction, Marshall Baxley strides toward me, his footpads clanging on the floor of the plane's cargo hold. He points a steel finger at my antenna. "Are you being a bad girl? Listening in on the Russian military communications?"

He's lowered the volume of his synthesized voice to a whisper, even though no one can overhear us. General Hawke and his deputies are in the C-17's cockpit, and the other soldiers are at the far end of the fuselage.

"No," I answer. "I'm watching video of the ground. It's a disaster down there. Half the city's in flames."

"Well, I've been eavesdropping on the Russians for the past two hours. It's a good thing I downloaded a translation program before we left Pioneer Base."

"What are they saying?"

"I'll tell you one thing, Russians love to curse. And they're very creative with their obscenities. You wouldn't believe all the names they've invented for-"

"Come on, Marshall. Spit it out."

"They're frantic because their weapons have stopped working. Their planes won't fly, their missiles won't launch, their tanks won't move. Needless to say, it's an upsetting situation."

I hear more clanging footsteps. DeShawn joins our little huddle. Jenny stays in the corner of the cargo hold, her turret turned toward the wall.

"What's going on?" DeShawn asks.

"The Russian army is paralyzed," Marshall reports. "When their mechanics opened up the stalled planes and tanks, they discovered that all the microchips in the vehicles had been shut down."

"Whoa, that's bad news." DeShawn's voice rises. "Must be Sigma, right?"

"You have amazing powers of deduction, DeShawn. Move to the head of the class."

"Man, I'm starting to hate that AI." He lets out a synthesized whistle. "It must've used its satellites to broadcast some nasty piece of software. Maybe a computer virus."

Marshall rocks his torso back and forth. It looks like he's nodding. "Yes, that would explain it. The satellites could've transmitted the signal to the antennas on all the Russian planes and tanks. Then the virus went straight to their microchips."

A disturbing thought occurs to me. "Wait a second. How come Sigma isn't doing the same thing to us? It could shut down this C-17 the same way, right?"

DeShawn shrugs, lifting his steel shoulders. "Maybe, maybe not. According to Hawke's databases, American military hardware is more advanced than the Russian gear. It's harder to infect our chips with computer viruses. But I bet Sigma's working on it."

"Well, let's just hope this plane gets to the airfield before Sigma figures it out."

Five anxious minutes later the C-17 touches down on the runway and coasts to a stop. The soldiers line up at the rear of the cargo hold, cradling their assault rifles. As soon as the cargo door opens, they bolt out of the plane and spread across the tarmac. I follow right behind, leading the Pioneers out of the aircraft. As their new commander, I guess I'm supposed to take the lead. Other than that, I have no idea what I'm doing.

The airfield is dark. The hangars beside the runway are silhouetted against the glow from the distant fires. I see signs of activity just beyond the hangars, and when I switch my camera to infrared, I glimpse a crowd of soldiers gathered around a pair of fifty-foot-high missiles. I scroll through my databases, trying to identify the tall rockets. They're not Russian, I discover to my surprise. They're U.S. Air Force interceptors, rockets designed to chase a ballistic nuclear missile after it's been launched. If the interceptors are fast enough, they can catch up to the nuke and destroy it in midflight.

DeShawn is beside me. His camera is also pointed at the American rockets, which stand on mobile launchers. "That must be the backup plan," he says. "If the Pioneers can't stop Sigma from launching the nukes, the Air Force will shoot 'em down."

"It's not much of a backup. Sigma has more than fifty nuclear missiles, and we have only two interceptors. And even those two won't fly if the AI infects them."

"Then I guess it's up to us, right? We'll just go to that computer lab and kick Sigma's butt."

DeShawn's voice is confident, almost cheerful. I'm jealous. "How can you be so calm?" I ask. "I'm a nervous wreck."

He lets out a synthesized chuckle. "Hey, I'm just happy to be alive, you know?"

Before I can respond, my acoustic sensor picks up the sound of squealing tires. I turn my turret toward the noise and see two big trucks skid to a stop on the runway. They're Russian army trucks, but they're rusted and ancient, at least thirty years old. Their extreme age explains why they're still running. Those trucks were built in the days before microchips became a standard feature in diesel engines. Because the old vehicles have no chips to infect, Sigma can't shut them down.

A dozen Russian soldiers jump out of the trucks and join the American soldiers on the tarmac. After a few seconds both groups head for the C-17 and start unloading the crates of equipment we brought from Pioneer Base. At the same time, General Hawke comes out of the plane and marches toward me.

"Gibbs!" he shouts. "Get your team together. We're going for a ride in those trucks."

"Are we driving to Tatishchevo, sir?"

Hawke nods. "After we cross the Volga we'll head for the woods outside Saratov. That's where we'll launch the Ravens. I want to start the assault by zero four hundred hours."

"Sir, can I ask a question? What are we going to do about Sigma's computer virus?"

Hawke hesitates before answering. "Where did you hear about that?"

"From monitoring the Russian communications. The virus is a problem, isn't it?"

He takes a deep breath, then points to the west, gesturing at the fires on the horizon. "Yeah, it's a problem. The computer virus crippled the whole Russian army. Then Sigma used its T-90s to blast the troops near Tatishchevo."

"But what about us? Could the virus shut down the Pioneers too?"

"Your control units have software firewalls. They'll stop any viruses from infecting your electronics. Unfortunately, I don't have as much confidence in our other military equipment, so we're upgrading the systems that are most vulnerable to tampering."

As Hawke says this, he glances at the interceptors on the other side of the airfield. I notice that some of his men are heading in that direction, carrying equipment from the C-17's cargo hold. I point at the soldiers. "You're upgrading the interceptors? They're vulnerable?"

Hawke hesitates again, clearly uneasy. "All I can say is that the Air Force had a problem with another missile. Let's leave it at that."

I don't like the sound of this. Hawke's hiding something from me, something big. "What kind of problem? Did Sigma tamper with the missile?"

The general shakes his head. "That's enough, Gibbs. Let's concentrate on our mission, all right?" He points at one of the Russian army trucks. "Get your Pioneers inside that vehicle. I'm gonna ride in the other truck with the Russian commander."

I keep my camera trained on Hawke as he marches away. My circuits are churning with suspicion. And fear too. A whole lot of fear.

Once Hawke is gone I turn my turret toward the other Pioneers. Marshall is a few feet behind me. I'm sure he overheard everything the general said. I step closer to him. "I need you to do some more eavesdropping," I whisper. "But not on the Russians."

"Let me guess," he whispers back. "You want me to listen in on the American communications channels?"

"You heard what Hawke said. About the problem with the missile. Find out what happened."

"If the information is classified, the communications will be encrypted. I'll need to break the code."

"But you can do that, right? You have the decryption software in your circuits?"

Marshall pats his armored torso. "It's all here, darling. Just give me a few minutes."

Inside the truck, the Russian soldiers keep their distance. They crouch on the other side of the truck's cargo hold, eyeing us with horror. I have to admit, their reaction upsets me. It's so different from what we experienced at Pioneer Base. The soldiers there saw us so often that they didn't cower or gape when we crossed paths in the base's corridors. And we, in turn, grew accustomed to their casual attitude. But the Russian soldiers haven't seen anything like us before, so their shock and fear are on full display. I'd almost forgotten what I'd become, but now they're reminding me. This is the reaction I'll always get when people see me for the first time.

I stand between Marshall and Jenny as the truck rumbles across the city of Saratov. Marshall is uncharacteristically quiet, probably because he's busy decoding communications, but he's not as quiet as Jenny, who hasn't said a word in the past twelve hours. To be honest, her silence is a little alarming. I know she's been struggling with depression ever since she became a Pioneer, but during our last days of training she seemed to be getting better. She started talking a bit, mostly gossiping about the other Pioneers. Although we never had any serious conversations, it was a good first step.

But Jenny clammed up after we left Pioneer Base. When I asked her what was wrong, she turned her turret away from me. At first I thought she was just scared, like the rest of us, scared of going into battle against Sigma. But now I'm not so sure. I sense that something else is troubling her.

The first half of the truck ride goes smoothly. We speed across the bridge over the Volga River, then barrel through the central part of Saratov. After ten minutes, though, my acoustic sensor picks up the thud of a distant explosion. We're approaching the western districts of the city, which are still being shelled by Sigma's T-90s. We get off the main highway and weave through the side streets, heading south to avoid the combat zone. After a few more minutes we leave the battle behind. I can still hear the explosions, but they're growing fainter.

I use my GPS software to pinpoint our location. We're driving through a hilly, wooded area between Saratov and Tatishchevo. The missile base is a huge installation that stretches across thirty miles of Russian countryside. The SS-27 nuclear missiles are scattered among the fields and forests, each rocket standing inside a hardened concrete silo, but Tatishchevo's barracks and supply depots are clustered at the central headquarters complex. That complex also includes our target, the base's computer lab.

Soon the trucks turn onto a dirt road that winds through the hills. I can't hear the explosions of the tank shells anymore. The noises of battle have faded into the background, muffled by the trees all around us.

Then Marshall breaks the silence. "Shannon. It was a Minuteman."

"What?"

"The American missile that Sigma tampered with. It was a nuke, a Minuteman III."

For a moment I think he's joking. He's kidding around, yanking my chain. But his voice doesn't have its usual sarcastic tone. For the first time ever, Marshall is completely serious.

I'm so scared I can't speak. I can't synthesize a word.

"Sigma launched the missile and changed its flight path," he adds. "It flew from North Dakota to Colorado. It hit Pioneer Base."

I start screaming. And so does Jenny.

CHAPTER.

19.

It's a sunny summer afternoon. I'm on the lawn behind our house in Yorktown Heights.

Wait a second. How did I get back home?

Two eight-year-old boys stand in front of me. One is short and red-haired. The other is tall and blond, but I can't see his face-it's just a blur, a patch of emptiness. I'm a little nervous facing these kids, but then a third boy claps his hand on my shoulder. He has blue eyes and a U-shaped scar on his chin. It's Ryan Boyd.