I stop running so as not to draw attention to myself and wander over toward the railing on the left-hand side of the walkway to get a better look. I lean against the railing with my back to him and then slowly turn.

At the moment his head is down. He has an attaché case on his lap with the lid open, both hands inside. Whatever he is doing, his attention is focused inside the case. He is wearing dark glasses and his face is shaded. Then suddenly he looks up, turns his head the other way, and for several seconds he stares across the street, not in the direction of the Supreme Court Building. Instead he is looking toward the Library of Congress, up high, toward the copper dome.

In that instant it clicks, the copper wings on the model plane. He has already landed the little brown bat. What it’s doing up there I have no idea. But there is no time left. Without thinking I push off from the railing and run straight at him.

Thorn hears my footfalls on the hard concrete and starts to turn his head. Running at full bore, six feet out from the bench I launch myself into the air.

Just as Thorn’s startled eyes turn to fix on me I roll my right shoulder into his upper body and smash into him.

The impact moves Thorn’s thumb on the computer track pad and sends the servomotor for the camera gimbal on the back of the little brown bat gyrating. The laser signal darts skyward just as the sensor in the bomb’s nose cone homes in. The servomotors on the canard and tail fins suddenly rotate, lifting the nose of the bomb from its sharp dive to a more flattened trajectory as the control surfaces bite into the air.

The impact of my body drives Thorn off the bench and sends both of us sprawling across the pavement. The attaché case flips into the air and slides across the concrete as the laptop flies out of it and skitters along the ground.

A woman screams and tourists suddenly move away from the bench as if it were the entrance to hell.

Even before he hits the pavement, Thorn’s hands are reaching out, trying to grab the flying computer as if it were a fumbled football. He hits the ground and instantly rolls up onto one knee.

Before I can move, he scrambles ten feet across the cement to the computer. Single-minded and focused, he tries to get his fingers on the controls.

Just as he picks up the computer and starts to finger the keyboard, a moving shadow crosses the ground. A whooshing sound streaks overhead. Thorn looks up, a kind of pleading expression in his eyes. Two seconds later a flash of light followed by a massive concussive explosion rocks the ground.

Joselyn connected with the dispatcher at 911, and reported that there was a bomb in the U.S. Supreme Court Building. She was watching, wondering what was happening, as she saw Paul race across the sidewalk maybe a hundred and thirty yards away, and careen into someone seated on a concrete bench.

“Who is this?” said the dispatcher. “I need your name.”

“There’s no time to talk,” said Joselyn. “Just evacuate the building and do it now!”

Before she could even press the button to hang up she felt the ground rock beneath her feet with the force of the explosion. Her gaze turned toward the flash of light and she saw the rising mushroom cloud as it billowed two hundred feet into the air little more than a half mile away.

The VRE, Virginia Rail Express, had just pulled out of Union Station, headed for Fredericksburg, in northern Virginia, when the blast ripped up the rails a quarter of a mile behind it.

The explosion sent a mound of dirt and debris high into the sky as the concussion rattled the trailing truck on the last passenger car off the rails. The slow-moving train immediately applied its brakes and came to a screeching halt as flames and an immense plume of black smoke rose into the sky just down the tracks behind the train.

With the concussive blast, all eyes around us suddenly turn away from the brawl on the concrete toward the north and the rising plume of smoke. A couple of women are screaming. A few of the tourists start to run. Others seem frozen in place.

I look into Thorn’s eyes. What I see is desperation and anger. Only he and I know that the collision on the bench and the massive explosion were connected.

He looks at me for only a second before he darts toward the sidewalk on First Street. Suddenly he realizes he has a chance to escape. He looks at me with a scowl, turns, and starts to walk away.

In an instant I’m on my feet.

He turns, sees me, and starts to run.

“Paul, let him go!” It’s Joselyn behind me, running to catch up. “Let the police get him.”

I turn, look at her. “Stay there!”

She cups her hands around her mouth. She’s still a hundred feet away. “Let him go. The police will find him.”

But by then it’s too late. Adrenaline has taken hold. I turn back toward Thorn, and with the chase instinct of a cat, I find myself in a footrace. We run down the sidewalk on First Street dodging tourists and government workers.

Thorn is maybe two hundred feet ahead of me, running at full speed. He reaches Independence Avenue and doesn’t even slow down. He runs out into the intersection against a red light, dodging cars with honking horns.

By the time I get there, he’s opened up a lead of almost half a block. I continue running. I can see him in the distance. Suddenly a car pulls up next to me. It’s a cab and Joselyn is in the back. She opens the door. “Get in!” she says.

I turn and look back at Thorn just as he runs between two barricades blocking cars from turning onto First Street across the intersection up ahead. “Go around and head him off,” I tell her. “Don’t get out of the car. Use the phone to call the police.”

She nods, slams the door closed, and the cab speeds away.

I continue running down the block until I reach the traffic barricade, then step between the two gates and start to jog again. I am in a canyon between two House office buildings, in the shade. I catch a fleeting glimpse of Thorn as he steps off the sidewalk to the right and disappears somewhere beyond the next intersection up ahead. I begin to wonder if he has a car parked in a garage or a lot. I pick up the pace and start to run.

As I clear the barricade at the other end of the block, I see the yellow cab coming this way. Now if he has a car we can follow him and call in the location to the cops. The cab screams up the street and stops at midblock. A few seconds later I reach it just as Joselyn is getting out of the backseat.

“I hope you have some money. All I have in my pocket is some change, a credit card, and my Metro pass,” she says. “And we’ll need that.”

“Why?”

“Hurry up. Pay the driver,” she says.

I do it and she grabs me by the hand, pulling me across the street. Then I realize where we’re going. The sign says CAPITOL SOUTH. It’s an open, cavernous concrete hole in the ground with escalators. We jump on the one going down.

“You sure he went in here?”

“I saw him,” she says. “I just hope he hasn’t gotten on one of the trains yet or we’ll lose him for good.”

The escalator drops into the bowels of the earth, maybe two hundred feet belowground. When we reach the underground station, it’s a milling madhouse with vending machines and a ticket kiosk that has a long line in front of it.

“Follow me.” Joselyn reaches into her pocket.

I stay right behind her.

She reaches the turnstile and slips a plastic card into the slot then steps through. She grabs the card as it’s spit out on the other side then reaches and hands it to me. I do the same and within seconds we’re running for the platform. I’m looking both ways, scanning the crowd to see if there’s any sign of Thorn.