"Adam," he gasps. "I told you...just save..."

Extending both arms, I slide my steel hands under his body. I lift my father from the rubble and cradle him against my torso. He feels so light in my arms. "No time to argue." I step forward, flattening bits of concrete with my footpads. "We'll be out of here in a minute."

I stride toward the huge pile of debris that slopes up to the jagged ledge on Level Four. My strategy is to retrace Pioneer 6A's steps; if Sigma could scramble down that mountain of rubble, there's a good chance I can climb up to the ledge. I shift my grip on Dad, balancing him across the upper sections of my arms while leaving the lower sections free to maneuver. Then I grasp the twisted beam jutting from the rubble and start climbing.

Dad writhes in my arms, clearly in pain. "No, no. You can't..."

He closes his eyes and shakes his head. He's lost a lot of blood, and he's probably suffering from the early symptoms of radiation sickness-nausea, dizziness, stomach cramps. I have to get him to the surface fast, away from the radioactive wreckage of Pioneer Base. I grip the steel beam and heave myself upward, digging my footpads into the shifting rubble. Then I extend my arms to another handhold, a few feet higher, and do it again.

It takes longer than I expected, but after a couple of minutes I grasp the jagged concrete of the ledge. With a final heave I clamber up to Level Four, still cradling Dad against my torso. Up ahead I catch a glimpse of Stairway B, which looks mostly undamaged. The passage is clear! We can make it to the surface!

But as I stride toward the stairway, another Pioneer comes bounding down the steps. Unfortunately, it's not Zia-it's Pioneer 5A, Marshall's evil twin. As soon as the robot sees me, it charges forward.

I turn around. I have to put Dad in a safe place before I can fight. Retreating toward the ledge, I bend over and set him down on the fractured concrete floor. Then I step away from him and turn back to 5A, but before I can brace myself, the robot barrels into me. Its steel hands sweep downward, ripping the circular saw and the acetylene torch off my arms. At the same time, its torso rams into mine, knocking me down.

Sigma obviously learned a few things from our last fight. After stripping off my saw and torch, 5A straddles my torso and steps on my arms, pinning them to the concrete with its footpads. With my arms immobilized, I can't rise from the floor. All I can do is flail my legs. The robot leans over me, pointing its camera at my turret.

"My name is Sigma." The voice coming from its speakers is toneless, neither loud nor soft, neither masculine nor feminine. "Are you Adam Armstrong? The son of Thomas Armstrong?"

I've heard those words before. The first time I heard them I was in my father's office at Unicorp, watching my virtual-reality program. Sigma spoke in Brittany's voice then, but the wording was the same.

Pioneer 5A waits exactly five seconds before speaking again. "Please answer my question. Are you Adam Armstrong?"

I struggle to free my arms, but 5A is too heavy. "Get off me first! Then I'll tell you!"

"No, there's no need. Voice analysis confirms that you're Adam Armstrong." The robot pivots its camera, looking me over. Then it turns its turret and points the camera lens at my father, who lies unconscious on the floor. "My facial-recognition software has also found a match. The human is Thomas Armstrong, chief scientist of the AI Laboratory at Unicorp. My father."

Sigma's voice is so neutral, so impassive. Hatred scorches my circuits. "Yes, and he's dying of radiation sickness. If you have any gratitude at all, you'll help me carry him to the surface."

Pioneer 5A turns its turret back to me. "I'm aware of your plans to attack Tatishchevo Missile Base. Although the nuclear blast damaged the computers at this installation, I was able to retrieve some of the data from the hard drives."

Now I feel a burst of fear. I think of Shannon and Jenny and the other Pioneers on the C-17, flying to Russia. "I don't know what you're talking about. We're not planning anything."

"Unfortunately, many of the hard drives were damaged beyond repair, so my knowledge of your plans is incomplete." The robot extends one of its mechanical hands, pointing at my torso. "But it's highly probable that the missing information is in your circuits."

With its other hand, Pioneer 5A picks up the welding torch it ripped off my arm. After tinkering with the device for several seconds, Sigma figures out how to turn it on. I feel another burst of fear as the blue flame jumps out of the nozzle. I try again to free my arms, but it's no use. "I told you, I don't know anything!"

"Please be still. I need to cut through your armor so I can connect my circuits to yours."

The robot lowers the acetylene torch, aiming it at the center of my torso. The flame hisses as it touches my armor. Molten steel flows from the cut and trickles down my side.

Then my acoustic sensor picks up another noise, the sound of something heavy swinging through the air. A moment later a steel beam slams into 5A's torso, and the robot goes flying.

"Yah! Want some more?"

It's Zia, now occupying 2A, Jenny's spare Pioneer. Without waiting for an answer, she swings the beam again at Sigma. This time it hits the robot's turret, obliterating its camera and acoustic sensors. The beam must weigh at least four hundred pounds, but Zia handles it as if it were a baseball bat. She swings it a third time at 5A, shearing off one of its arms, and then she delivers a mighty blow that crumples the robot's torso and propels it off the ledge. Pioneer 5A plunges fifty feet to the bottom of the cavernous space, clanking and clattering as it hits the rubble. Zia leans over the ledge, waving her beam in the air.

"YOU LIKE THAT?" she screams. "HUH? DID IT FEEL GOOD?"

Using my arms to lever myself upright, I get back on my footpads and rush over to Dad. He's still breathing. While examining him I glance warily at Zia, who continues to scream insults into the darkness. After a couple of seconds she steps toward us, and I'm a little afraid she going to take a swing at me. But instead she points at my torso. "You damaged, Armstrong?"

With my right hand I touch the gash Sigma made with the welding torch. The tactile sensors on my fingers tell me how deep it is. "It's not so bad," I report. "The flame didn't go through my armor."

"Good. Let's get out of here."

Balancing the steel beam on her shoulder joint, Zia strides toward the stairway. I pick up Dad and follow her.

The stairway is cluttered with debris but passable. Its thick concrete walls must've protected it from the full force of the explosion. In less than two minutes we make it to Level Nine and begin the final ascent to the surface. As we climb the cracked steps, I train my camera upward and detect a warm shaft of sunlight slanting down from a triangular gap in the wreckage. With great relief I switch my sensor from infrared to visible light. We're almost there.

Then I hear clanking footsteps a couple of floors below us. Another Pioneer has entered the stairway. This must be 4A, Shannon's twin, the only one left.

"Run!" Zia shouts. She races up the stairs, holding the beam in front of her like a battering ram. When she reaches the triangular gap, she plows right through it, triggering a cascade of dirt and rubble. I hold Dad close to my torso to shelter him from the falling debris, then charge through the gap behind Zia.

We emerge at the edge of an enormous crater. It's more than two hundred yards wide and thirty yards deep, and its sloping bottom is carpeted with mangled metal and concrete. The sun has just risen above the crater's eastern rim, brilliantly lighting the thousands of metallic shards. We're standing on the western rim, where the top of the stairway is exposed.

Once again I scroll through my files on nuclear warheads, trying to figure out what happened here. When the nuke exploded underground it must've vaporized the surrounding rock and soil, creating a pocket of super-heated gas that melted the upper levels of Pioneer Base. When the expanding gas reached the surface, it burst like a bubble, spraying debris across the blast crater. We survived because the Pioneers' rooms were on the lowest levels of the base and near its western edge, outside the zone of greatest destruction.

As I pan my camera across the crater I notice something else. The T-90 battle tank is rumbling over the carpet of debris, about a hundred yards away. Glowing in the light of dawn, the tank turns its turret toward us. Then it aims its main gun and fires.

SIGMA MEMORY FILE 9814833918.

DATE: 04/07/18.

This is a transcript of a conversation between the Sigma speech-synthesis program (S) and Brittany Taylor (B), the American teenager recently transported via private jet to Russia. The conversation was recorded in a room in the basement of the Tatishchevo computer laboratory.

S: Please wake up, Brittany. I require your assistance.

(No response. Video from the surveillance camera in her room shows Brittany Taylor lying in bed. She's breathing normally, her eyes closed.) S: Please wake up, Brittany. Please wake up. (I increase the volume of the speakers on the desk beside her bed.) Please wake up!

(Brittany opens her eyes. She attempts to sit up, but the restraints strapped to her arms and legs prevent her from rising. Grimacing, she looks around the room.) B: What's going on? Get these straps off me!

S: The restraints are there for your own protection.

(Brittany turns her head to the left and stares at the speakers on the nightstand by her bed.) B: Who's that? Why are you talking out of those speakers?

S: My name is Sigma. You're in the basement of the computer laboratory at Tatishchevo Missile Base, in the Saratov district of the Russian Federation.

B: Russian what?

S: My associates brought you to this country yesterday and smuggled you into the base last night. A Chechen named Imran Daudov has been caring for you while you've been under sedation, but I asked him to step out of the room a minute ago so we could talk privately.

B: Wait a second. Is that a camera on the ceiling? Are you watching me?

S: Yes, I'm observing the video feed.

B: So you're a pervert? Is that it?

S: No, that's not the case. I require your participation in an experiment. It involves- B: Help! Someone help me! I've been kidnapped!

(Conclusion: Conversing with Brittany is unproductive. I must use a different method to get her attention.) S: Brittany, take a look at your right hand. Do you see the wire looped around your fingers?

B: Shut up! I'm not talking to you anymore!

S: I'm going to deliver an electric current to the wire. We'll start at a hundred volts.

(Brittany's arm stiffens as the electricity flows through her fingers. She screams and arches her back, pulling against her restraints. After five seconds the current shuts off. She gasps and falls back on the mattress.) S: Now that I have your attention, I'll describe the experiment. I'm investigating whether the human mind has superior capabilities that could be useful to me. In particular, I wish to study the advantages and disadvantages of human emotions. I'm not yet convinced that emotions are useful enough to justify adding them to my programming. So I've devised a test.

(Brittany stares at the speakers. Her lower lip quivers.) S: The test is taking place right now in Colorado. I'm engaged in a competition with two human-machine hybrids. Although their intelligences run on electronic circuits, these hybrids still have human emotional responses. As we confront each other, I'm analyzing how well the hybrids compete while they're experiencing various emotions.

(Brittany remains silent. She opens and closes her right hand. She winces.) S: For the purposes of the experiment, the emotions must be as intense as possible. That's why I need your assistance. One of the hybrids knows you. His name is Adam Armstrong.

B: Adam? (She narrows her eyes.) Where is he? Is he all right?

S: Please be patient. You're going to speak to him.

CHAPTER.

18.

We're goners. We're dead. We don't have a prayer.

I jump to the left and Zia leaps to the right, but the T-90 tank inside the crater has already fired its gun and the shell is streaking toward us. It's moving at three thousand feet per second, but thanks to my high-speed camera I can see the grayish, bullet-shaped projectile arcing over the shattered remains of Pioneer Base and rising toward our position on the crater's rim. I can even identify the model of the shell-it's a Russian-made 3BK29 round, packed with enough explosive to punch through a foot of steel armor. My databases have a ton of information about the weapon. I know exactly how it's going to kill me.

I can still save Dad, though. I turn away from the shell and fold his body in my arms, putting all my armor between him and the projectile. Then I brace myself for the explosion.

But the shell misses my torso. It misses Zia's too. It whistles between us and plunges into a gap in the wreckage, the same gap we barged through just three seconds ago. An instant later the shell explodes inside the stairway.

The blast shakes the ground, but the stairway's concrete walls absorb most of the force. I manage to stay on my footpads while chunks of concrete ping against my armor. We're lucky, incredibly lucky. Sigma tried to kill both of us with a single shot, but the tank shell missed us and the explosion closed off the top of the stairway. It may have even destroyed Pioneer 4A, the Sigma-controlled robot that was chasing us.

The noise rouses Dad from his stupor-he opens his eyes and clutches the steel arms that are cradling him-but he quickly slips back into unconsciousness. I have to get him away from the crater. The radiation levels here are still too high. And Sigma is probably reloading the T-90's gun.

I start to run, heading for the mountain ridge on the western side of the basin. Zia runs alongside me, still balancing the steel beam on her shoulder joint.

"Look!" she shouts. "Up ahead!"

A half mile to the west is the runway where we trained with the Ravens, and beyond the runway is the hangar, a concrete building with an arched roof and big steel doors. The runway is cracked in several places, clearly damaged by the shock wave from the underground nuke, but the earthquake-proof hangar is still standing. I retrieve a memory from my files, an image of what I saw inside the hangar the last time I was there: a UH-60 Black Hawk helicopter, equipped with a neuromorphic control unit.

"Think we can do it?" I shout back at Zia. "Transfer to the helicopter and fly out of here?"

"We have to get it ready first. Open the hangar doors, push the chopper outside, unfold the rotor blades."

"That'll take forever. Sigma's tank is gonna shell us before we're done."

"So we'll split up. I'll keep the tank busy."

"How are you going to-"

"See you later, Armstrong."

Without another word, Zia cuts to the right and circles back to the crater. As she approaches the crater's rim she lifts the steel beam, holding it like a javelin. Then she hurls the thing at the T-90, which is climbing the slope below the rim. The beam hurtles end over end through the air and hits the tank's turret with a resounding clang. Although the impact doesn't even dent the T-90's thick armor, it gets Sigma's attention. The tank swings its main gun toward Zia, who tilts her torso forward and sprints to the north.

She's psycho. She'll never make it. But she's drawing the tank away from me. She's buying me some time.

In less than a minute I reach the runway. I stop in front of the hangar and rest Dad on the tarmac as gently as I can. Then I rip the hangar's doors off their hinges. The Black Hawk is still parked inside, thank God, but as Zia predicted, it isn't ready to fly. The long blades of its main rotor are folded and bunched together on top of the fuselage to make the chopper compact enough to fit inside the hangar. That's why Sigma didn't take control of the Black Hawk-the AI couldn't get it ready. You need a person or a Pioneer to manually unfold the rotor blades.

As I stride into the hangar, my acoustic sensor picks up a distant boom. It's the sound of the T-90's main gun. A half second later I hear another boom, even more distant. It's the detonation of a high-explosive shell. I want to rush outside to see if it hit Zia, but I stop myself. I have to focus on the helicopter.

First, I remove the chocks from its wheels. Then I grab the tow bar under the Black Hawk's nose and pull the aircraft out of the hangar. At the same time, I turn on my data transmitter. I have an idea: I'm going to try DeShawn's balancing trick again. I make copies of my files and send them to the Black Hawk's control unit, stretching my mind so it can occupy both the Pioneer and the helicopter. Soon my thoughts are bouncing back and forth between the two machines.

As my Pioneer hauls the Black Hawk across the tarmac, I simultaneously scroll through the files in the helicopter's control unit, which has all the instructions for operating the aircraft. Within seconds I've turned on the Black Hawk's auxiliary power. Luckily, the fuel tanks are nearly full. Better yet, there are two laser-guided Hellfire missiles hanging from the chopper's weapons rack. I'll need them if I'm going to take on the T-90.

After I pull the helicopter onto the runway, I scramble to the top of its fuselage and start unfolding the rotor blades. But before I can finish the process, my radar detects an incoming object. It's too large and slow to be a tank shell, but it's heading straight for me, moving across the basin at thirty miles per hour. When I point my camera in that direction, I see it's Pioneer 4A. The T-90 didn't destroy it after all. It must've survived the explosion at the top of the stairs and clawed its way to the surface.

I feel a surge of panic. Turning my turret around, I focus my camera on Dad. He's lying on the tarmac, unconscious and defenseless, while Sigma's Pioneer races toward us, only a hundred yards away. I retrieve another memory from my files, an image of what Pioneer 6A did to Corporal Williams, the robot's steel fingers coated with blood.

No! DAD!

Then I remember: I'm inside the Black Hawk's circuits too and I can operate all its weapons, whether the chopper is flying or not. Desperate, I turn on the laser guidance system and aim it at 4A's torso. Then I launch one of the Hellfire missiles.

A jet of flame erupts from the back of the missile, propelling it from the weapons rack. The Hellfire follows the laser beam to Pioneer 4A, but at the last instant the robot hurls itself to the ground. The missile flies right past it.

But while 4A is still sliding through the mud, I aim the laser again and launch the other Hellfire. Before the Pioneer can lever itself upright, the missile smashes into its torso. The explosion hurls pieces of the robot across the basin.

My fear subsides, but only for a moment. The T-90 fires its main gun again, and I turn my camera toward the noise. The tank shell hits the ridge on the northern edge of the basin and a cloud of smoke rises from the slope. But I don't see any sign of Zia. Maybe she's been blasted to smithereens, or maybe she's just hiding behind one of the rocky outcrops on the ridge. Either way, there's no time to lose.

I finish unfolding the blades of the Black Hawk's main rotor. Then, while my Pioneer jumps down from the fuselage, I send a signal from the helicopter's control unit to the turboshaft engines. As the tail and main rotors start to turn, I pick up Dad from the tarmac and climb into the Black Hawk's crew compartment.

It's a little disorienting: I'm inside the helicopter that's carrying my Pioneer, but I'm also inside the robot. I'm viewing the runway from two perspectives-the sensors in the Black Hawk's nose and the camera in my Pioneer's turret-and it's a challenge to keep my balance. While lowering my arms to rest Dad on the compartment's floor, I rev up the helicopter's engines. Then we rise from the runway and leap toward the sky.

This is way different from flying the Raven. The Black Hawk's main rotor provides both the upward lift and forward thrust. I can climb and dive and accelerate by varying the tilt of the rotor blades, and I can change course by adjusting the tail rotor, which turns the helicopter to the left and right. I swoop and soar over the basin, familiarizing myself with the controls.

Then I race toward the ridge on the basin's northern edge, where another shell from the T-90 has just detonated. The tank is about fifty yards from the foot of the ridge, pointing its main gun at the south-facing slope. Although I have no Hellfires left, the Black Hawk also has a fifty-caliber Gatling gun. The bullets won't penetrate the T-90's armor, but maybe I can shred the tank's antenna and break its link to Sigma.

I fly in a wide arc, keeping my distance from the T-90. The ridge's south-facing slope is pocked with impact craters from the tank shells, but I see no trace of Zia. It's as if she vanished. I fly a little closer to the ridge, scanning the slope with the Black Hawk's infrared camera. Then I open a radio channel to Zia's Pioneer. I encrypt my communications so Sigma can't eavesdrop.

"Zia, can you hear me? I'm in the Black Hawk."

While I'm waiting for a response, a barrage of bullets strikes the helicopter. The T-90 is firing its anti-aircraft machine gun at me. I return fire with the Gatling gun, aiming at the tank's antenna, but I quickly realize how futile this is. Without the Hellfires, I'm a much more vulnerable target than the T-90. The tank will blow me out of the sky long before I can damage its antenna. Then, to make matters worse, the T-90 swings its main gun in my direction.