And all it cost was a buck or two.

Not a bad deal.

He glanced into his wallet. All twenties. He had just cashed up at an ATM at the

Metro station. He shrugged and tugged out a bill with Andrew Jackson's face.

Okay, sometimes it cost more than a buck or two.

He lifted his head just as the two met. Gray reached out with the twenty-dollar bill but found the man's hand wasn't empty. Resting in the middle of his palm lay a tarnished coin, about the size of a fifty-cent piece.

Gray frowned.

It was the first time a homeless man had tried to pay him.

Before he could comprehend the situation, the man tripped toward him, as if suddenly shoved from behind. His mouth opened in an O of surprise. He fell into

Gray, who reflexively caught the elderly man.

He was lighter than Gray had expected. Under his jacket, the man's body seemed all bone, a skeleton in a suit. A hand grazed Gray's cheek. It burned feverishly hot. A flicker of fear of disease, of AIDS passed through Gray, but he did not let go as the man slumped in his arms.

Carrying the man's weight, Gray shifted his left arm. His hand settled upon a hot welling wetness on the man's lower back. It streamed over his fingers.

Blood.

Gray pivoted on instinct. He hip-rolled to the side and dove off the sidewalk, with the man still clutched in his arms. The thick grass cushioned their fall.

Gray didn't hear the next shots but two ricocheting flashes sparked off the concrete sidewalk where he'd been standing. Without stopping, he continued to roll until he reached a metal-and-concrete sign planted in the lawn of the

Smithsonian Castle. It stood only waist high. He huddled behind it with the old man. The sign read: SMITHSONIAN INFORMATION CENTER IN THE CASTLE.

Gray certainly needed information.

Like who was shooting at him.

The solid sign stood between him and the Mall. It offered temporary shelter.

Only ten yards away, the arched doors of a side entrance of the Smithsonian

Castle beckoned. The building itself rose in turrets and towers of red sandstone, all quarried from Seneca Creek, Maryland, a true Norman castle, a literal fortress. The protection it offered lay only a few steps away, but to cross that open distance would leave them exposed to the sniper.

Instead, Gray yanked a pistol a compact Sig Sauer P229 from the holster at his back. Not that he had a target. Still, he readied his weapon in case there was any direct assault.

At Gray's side, the homeless man groaned. Blood soaked his entire back. Gray frowned at the man's continuing misfortune in life. The poor sack had come seeking a bit of charity and got a bullet in the back instead, collateral damage in an assassination attempt against Gray.

But who was trying to kill him? And why?

The homeless man lifted a palsied arm, failing with each ragged breath. From the entry point and amount of blood, the shot had struck a kidney, a fatal wound for one so debilitated. The man reached to Gray's thigh. His fingers opened to drop the tarnished coin he had been holding. He had somehow kept his grip on it. The coin bounced off Gray's leg and rolled to the grass.

A final gift.

A bit of charity returned.

With the deed done, the homeless man's limbs went slack. His head fell to Gray's shoulder. Gray swore under his breath.

Sorry, old man.

His other hand freed his cell phone. Thumbing it open, he hit an emergency speed-dial button. It was answered immediately.

Gray spoke rapidly, calling a mayday into central command.

Help's on the way, his director announced. We have you on camera outside the

Castle. Seeing lots of blood. Are you injured?

No, he answered curtly.

Stay put.

Gray didn't argue. So far no further shots had been fired. No ringing impacts against the sheltering sign. There was a good chance the shooter had already fled. Still, Gray dared not move not until the cavalry arrived.

Pocketing his cell phone, Gray retrieved the man's coin from the grass. It was heavy, thick, crudely minted. He lifted it and absently rubbed at its surface.

Using the dead man's blood on his fingers, he polished the grime off the surface to reveal an image of what appeared to be a Greek or Roman temple, six pillars under a peaked roof.

What the hell?

In the coin's center stood a single letter.

Gray thought it was the Greek letter ?.

Sigma.

In mathematics, the letter sigma represented the sum of all parts, but it was also the emblem for the organization Gray worked for: Sigma, an elite team of exuSpecial Forces soldiers who had been retrained in scientific fields to serve as a covert military arm for DARPA, the Defense Department's Advanced Research

Projects Agency.

Gray glanced to the Castle. Sigma's headquarters were here, buried beneath the foundations of the Smithsonian Castle in former World War II bunkers. It was perfectly situated to take advantage of the proximity to the halls of government, the Pentagon, and the various private and national laboratories.

Focusing back on the coin, Gray suddenly realized his mistake. The letter was not a Greek ? but merely a large capital E. In his panic, his eyes had played tricks, seeing what had been forefront in his mind.

He closed his fist over the coin.

Just an E.

It wasn't the first time in the past few weeks that Gray had assumed connections that weren't there or at least that was the consensus among his colleagues. For a solid month, Gray had been searching for some confirmation that a lost friend,

Monk Kokkalis, could still be alive. But so far, even utilizing the full resources of Sigma, he had reached only dead ends.

Chasing ghosts, Painter Crowe had warned after the first weeks.

Maybe he was.

Across the way, doors crashed open in the front of the Castle. A dozen black-suited figures fled outward with weapons raised, clutched near shoulders in double grips.

The cavalry.

They moved cautiously, but no one fired shots at them.

They reached Gray's side quickly and flanked around protectively.

One of the men fell to a knee beside the homeless man. He dropped a paramedic's pack, ready to offer aid.

I think he's gone, Gray warned.

The medic checked for a pulse, confirming Gray's assessment.

Dead.

Gray climbed to his feet.

He was surprised to see his boss, Painter Crowe, at the side entrance.

Jacketless, his sleeves rolled to the elbows, Director Crowe shoved through the door. His expression was stormy. Though ten years older than Gray, Painter still moved like a lean-muscled wolf. The director must have assessed the risk to be minimal. Or maybe, like Gray, he merely sensed that the sniper had already fled.

Still, what didn't the man understand about desk job?

Painter crossed to him as sirens sounded from the distance. I have local P. D. locking down the Mall, he said in clipped tones.

Too little, too late.

Most likely. Still, ballistics will narrow down a trajectory radius. Figure out from where the shots were fired. Was anyone following you?

Gray shook his head. Not that I could assess.

Gray read the calculations in the director's eyes as he surveyed the Mall. Who would attempt to assassinate Gray? On their own doorstep. It was a clear warning, but against what? Gray had not been active in any operation since the last mission in Cambodia.

We already pulled your parents into security, Painter said. Just as a precaution.

Gray nodded, grateful for that. Though he could imagine his father was not too happy. Nor his mother. They had barely recovered from a brutal kidnapping two months ago.

Still, with the immediate threat waning, Gray turned his attention to who might have tried to kill him and more important, why. One possibility rose to the forefront: his current line of inquiry. Had his investigation into his friend's fate struck a nerve somewhere?