"And now it's a museum," Gray said.

"As of 1935," Vigor confirmed, and pointed to the scaffolding on the south side of the structure. "Restoration work has been almost continuous since that date. And not just on the outside. When Sultan Mehmed converted the church to a mosque, he plastered over all the Christian mosaics, as it is against Islamic law to depict human figures. But over the past decades, there's been a slow and meticulous attempt to restore those priceless Byzantine mosaic murals. At the same time, there's been an equal desire to preserve the ancient Islamic art from the fifteenth and sixteenth centuries, impressive sweeps of calligraphy and decorated pulpits. To balance such a project, the restoration work at Hagia Sophia required bringing in experts from all fields of architecture and art. Including consulting the Vatican."

Vigor led the way across the open plaza toward the arched entrance, following the flow of tourists. "As such, I thought that I might bring someone familiar with restoration, someone who has been consulted by Hagia Sophia's curators in the past."

Gray remembered Vigor mentioning that he had sent someone ahead to begin the hunt for the golden needle in a massive Byzantine haystack.

As they reached the doors, Gray noted a bearded giant of a man inside the door, blocking the flow of tourists. He stood with his fists on his hips, glowering at everyone. But when he spotted Vigor, he raised an arm in greeting.

Vigor motioned him back into the depths of the church.

Gray followed, anxious to get off the streets, unsure if any of the Guild trackers had reached their location. Until his parents were safe, he didn't want to rankle Nasser in any way, to make the man question Seichan's earlier subterfuge.

Passing through the door, Gray glanced back toward the open plaza. He saw no sign of Seichan or Kowalski. Their two parties had separated as soon as they left the hotel. Seichan had purchased a prepaid throwaway cell phone. Gray had memorized her number. It was the only way of contacting her.

"Commander Gray Pierce," Vigor introduced, "this is my dear friend Balthazar Pinosso, dean of the art history department at the Gregorian University."

Gray's hand was swallowed up by Balthazar's grip. He stood just shy of seven feet.

Vigor continued, "Balthazar was the one who first discovered Seichan's message in the Tower of Winds and helped me with the angelic translations. He's also good friends with the museum's curator here."

"Lot of good that'll do," Balthazar groused in a deep baritone, and led the way into the main church. He waved an arm ahead. "We've got a lot of ground to cover."

The man stepped aside and the view opened.

Gray gaped at the sight. Vigor noted his reaction and patted him on the shoulder.

A long barreled vault stretched a vast distance ahead, not unlike entering a train station. Overhead, a series of arches and cupolas climbed to the central main dome. A second-floor colonnade framed both sides. But the most impressive sight was not anything constructed of stone—it was simply the play of light in the space. Windows pierced walls and lined the bottoms of domes, allowing sunlight to reflect off emerald-and-white marble, off gold-encrusted mosaics. The sheer volume of empty space, unsupported by interior pillars, seemed impossible.

In awed silence Gray followed the two men down the long nave.

Reaching the heart of the church, Gray stared up at the scalloped vault of the main dome, twenty stories over his head. Its ribbed surface was decorated with rippling gold-and-purple calligraphy. Around its bottom circumference, forty arched windows allowed in morning sunlight, creating an appearance that the dome was hovering over one's head.

"It's like it's floating up there," Gray mumbled.

Balthazar joined him. "An architectural optical illusion," the art historian explained, and pointed up. "See those ribs along the underside of the roof, like the braces on an umbrella? They distribute the weight around the windows down to the flared pendentives seated atop massive foundation piers. Also the roof itself is lighter than it appears, constructed of hollow bricks kilned in Rhodes from the city's porous clay. It's a masterpiece of illusion. Stone, light, and air."

Vigor nodded. "Even Marco Polo was awed, to quote the great man, by 'the apparent weightlessness of the dome, and the bewildering abundance of direct and indirect lighting effects.'"

Gray understood. It was also strange to know that where he now stood, Marco Polo had also stood, the two men joined across the ages by their mutual wonder at and respect for the ancient builders.

The only blemish to the effect was the wall of black scaffolding along one side that climbed from the marble floor to the top of the dome.

It helped bring Gray back to his situation. He checked his watch. Nasser would be arriving before nightfall. They had less than a day to solve this riddle.

If his plan was going to work . . .

But where to start?

Vigor was asking the same of his friend. "Balthazar, were you able to question the museum staff? Has anyone seen anything like angelic script in here?"

The man rubbed his beard and sighed. "1 interviewed the curator, talked to his staff. The curator knows Hagia Sophia from its underground crypts to the tip of its highest dome. He insists nothing like angelic script can be found anywhere. He expressed one thought, though . . . something you're not going to like to hear."

"What?" Vigor asked.

"Remember how much of Hagia Sophia was plastered over from when the church was converted into a mosque. What we may be looking for could be hidden under inches of old plaster. Or it could have been inscribed on plaster that has since been cleaned away." Balthazar shrugged. "So there's a very real possibility that what we seek may be gone."

Gray refused to believe it. While Vigor and Balthazar discussed such matters in more detail, he walked away. He needed to think. He checked his watch again, a reflexive gesture. Nervous and worried. He didn't even really see the time. He dropped his arm and crossed to the scaffolding. He should never have left his parents alone. His mother's few words over the phone haunted him.

I'm sorry. Your father. I needed his pills.

Something must have happened. Gray had refused to take into account his father's illness, his need for medication. Was his neglect a purposeful blindness, a refusal to accept his father's true condition? Either way, his recklessness now threatened his parents' lives.

Gray sank down, cross-legged, and stared up toward the dome. He fought to clear his mind. His worries, fears, and doubts would not serve him. Or them. Taking a deep steadying breath, he exhaled slowly and let the drone of the tourists fade into the background.

He pictured the church as it must have looked back in the sixteen-hundreds. In his mind, he repainted the walls again, whitewashing over the golden mosaics with plaster. He did so with concentrated deliberation. A meditative exercise. If only in his head, the old mosque came alive again. He heard the muezzin calling from the minarets over the ancient city. He pictured the supplicants knelt atop rugs, rising and falling, in faithful prayer.

In such a place, where would the next key be hidden? Where in all this vast space, with its countless anterooms, galleries, and side chapels?

As he sat, Gray spun his view of the church behind his eyes, like a three-dimensional computer model, studying it from all angles. As he did so, his finger absently traced in the plaster dust on the floor. He finally became aware of what he was drawing: the glyph of angelic script, the one inscribed on the back of Marco's golden passport.

He stared down at the single letter while still spinning the architectural structure of Hagia Sophia around in his head.

"It was already a mosque," he mumbled.

He tapped the four circles, what Vigor called diacritical marks.

Four circles, four minarets.

What if the symbol was more than the first key to solving the riddle of the coded map? What if was meant also to be a clue leading to the second key? Didn't Seichan say something about that? How the one key would lead to the next?

In his mind's eye, he superimposed a schematic of Hagia Sophia over the symbol, positioning the minarets so it overlaid the diacritical marks. Four circles, four minarets. What if the symbol was supposed to also represent Hagia Sophia? A crude map with the minarets as anchors.

If so, then where to begin looking?

In the dust, Gray added an additional dotted line.

"X marks the spot," he mumbled.

11:02 A.M.

Vigor noted Gray crawling on his hands and knees near the center of the nave, sweeping the marble floor with his hands.

Balthazar noted the man's actions with a raised eyebrow.

The two men crossed over to Gray's side.

"What are you doing?" Balthazar said. "If you're planning on checking the entire floor by hand, you'll be here for weeks."

Gray sat back, stared up at the dome as if gauging his position, then continued his sweep of the floor, working along the edge of the scaffolding. "It has to be here somewhere."

"What?" Vigor asked.

Gray pointed back to where he had originally been seated. Vigor strode over and stared down at the smudged drawing in the dust. His brow crinkled.

Gray spoke. "It's a rudimentary map of Hagia, indicating where we should be searching for the next clue."

Vigor sensed the truth of Gray's assessment, surprised yet again at the man's unique ability to cogitate and analyze. It slightly frightened him.

Gray continued to crawl, slowly working a specific section of the floor, gaining a few strange glances from some passing tourists.

Balthazar tracked at his heels. "You think someone carved a bit of angelic script into the marble."

Gray stopped suddenly, his shoulder brushing the black scaffolding. He fingers returned to a spot he had just swept over. He leaned down and blew on the tile.

"Not angelic script," Gray said, and reached to his shirt collar.

Vigor joined him. Both he and Balthazar knelt around the tile that intrigued Gray. Reaching out, Vigor felt the marble with his fingertips.

Faintly inscribed in the tile, worn by ages and the erosion of treading feet, was the barest outline of a cross.