Not today. When he finished the first copy, the crucial one, he compared it to what he had sung. It was as if he had seen the words of the hymn before him as he wrote. Here they were again, as pure and perfect as when the Lord had given them to him. He bent his head in thanksgiving.

He took more papyrus and began the second and third copies. Usually when he was copying, his eyes went back to the original every few words. Now he hardly glanced at it. He had no need, not today.

He was no fine calligrapher, but his hand was clear enough. After so long at Ir-Ruhaiyeh, writing from left to right had even begun to seem natural to him.

The bell rang for evening prayer. The monk noticed, startled, that the light streaming in through the window was ruddy with sunset. Had his task taken any longer, he would have had to light a lamp to finish it. He rubbed his eyes, felt for the first time how tired they were. Maybe he should have lit a lamp. He did not worry about it. Even if the light of the world was failing, the light of the Holy Spirit had sustained him while he wrote.

He took the three copies of the hymn with him as he headed for the chapel. John, he knew, would be pleased that he had finished writing in a single afternoon. So much still remained to be done before the monks left Ir-Ruhaiyeh.

Donkeys brayed. Horses snorted. Camels groaned, as if in torment. Isaac knew they would have done the same had their loads been a single straw rather than the bales and panniers lashed to their backs. The abbot stood outside the monastery gates, watching monks and beasts of burden file past.

The leave-taking made him feel the full weight of his years. He rarely felt them, but Ir-Ruhaiyeh had been his home all his adult life. One does not abandon half a century and more of roots without second thoughts.

Isaac turned to John, who stood, as he so often did, at the abbot’s right hand. “May it come to pass one day,” Isaac said, “that the Persians be driven back to their homeland so our brethren may return here in peace.”

“And may you lead that return, Father Abbot, singing songs of rejoicing in the Lord,” John said. The prior’s eyes never wandered from the gateway. As each animal and man came by, he made another check mark on the long roll of papyrus he held.

Isaac shook his head. “I am too old a tree to transplant. All other soil will seem alien to me; I shall not flourish elsewhere.”

“Foolishness,” John said. For all his effort, though, his voice lacked conviction. Not only was he uneasy about reproving the abbot in any way, he also feared that Isaac knew whereof he spoke. He prayed both he and his superior were wrong.

“As you will.” The abbot sounded reassuring-deliberately so, John thought. Isaac knew John had enough to worry about right now.

The procession continued. At last it came to an end: almost three hundred monks were trudging west in hope and fear. “Is everyone safely gone?” Isaac asked.

John consulted his list, now black with checks. He frowned. “Have I missed someone?” He shouted to the nearest monk in the column. The monk shook his head. The question ran quickly up the line, and was met everywhere with the same negative response.

John glowered down at the unchecked name and muttered under his breath. “He’s off somewhere devising another hymn,” the prior growled to Isaac. “Well and good-on any day but this. By your leave-” He started back into the now-abandoned monastery.

“Yes, go fetch him,” Isaac said. “Be kind, John. When the divine gift takes him, he forgets all else.”

“I’ve seen.” John nodded. “But even for that we have no time today, not if we hope to stay in this world so God may visit us with His gifts.”

Entering Ir-Ruhaiyeh after the monks had gone out of it was like seeing the corpse of a friend-no, John thought, like the corpse of his mother, for the monastery had nurtured and sheltered him as much as his fleshly parents had. Hearing only the wind whistle through the courtyard, seeing doors flung carelessly open and left so forever made John want to weep.

His head came up. The wind was not quite all he heard. Somewhere among the deserted buildings a monk was singing quietly to himself, as if trying the flavor of words on his tongue.

John found him just outside the empty stables. His back was turned, so even as the prior drew near he caught only snatches of the new hymn. He was not sure he was sorry. This song seemed to be the complement of the one the monk had created in the refectory; instead of praise for the Lord, it told of the pangs of hell in terms so graphic that ice walked John’s back.

“For the unbelievers, for the misbelievers, the scourge. Their hearts shall leap up and choke them. Demons shall seize them by feet and forelocks. Seething water shall be theirs to drink, and-” The monk broke off abruptly, jumping in surprise as John’s hand fell on his shoulder.

“Come, Brother Mouamet,” the prior said gently. “Not even for your songs will the Persians delay. Everyone else has gone now; we wait only on you.”

For a moment, he did not think the monk saw him. Then Mouamet’s face cleared. “Thank you, reverend sir,” he said. “With the Lord giving me this hymn, I’d forgotten the hour.” The abstracted expression that had raised awe in John briefly returned. “I think I shall be able to recover the thread.” “Good,” the prior said, and meant it. “But now-”

“-I’ll come with you,” Mouamet finished for him. Sandals scuffing in the dust, they walked together out of the monastery and set out on the long road to Constantinople.

I’ve written a series of stories set in a world where Muhammad, instead of founding Islam, converted to Christianity on a trading mission into Syria and ended his days a monk (the previous tale in this book, “Departures,” shows his monastic life; a later one here will look at that world several hundred years after his conversion). The world of “Islands in the Sea” looks at the other side of the coin and considers what things might have been like had the Byzantine Empire, instead of shielding southeastern Europe from Islam for hundreds of years, collapsed under the weight of an early Arab onslaught. In our history Muslim forces twice besieged Constantinople, in 674-78 and 717-18, but the Byzantine capital held and the Empire survived as Christianity’s eastern bulwark, holding Islam out of Anatolia and the Balkans for centuries to come while converting the Bulgars and Russians to faith in Christ. But what if the Empire had fallen in the eighth century instead of the fifteenth? The still-pagan folk to the north of Constantinople would have had new choices to make

The Bulgar border guards had arrows nocked and ready as the Arab horsemen rode up from the south. Jalal ad-Din as-Stambuli, the leader of the Arab delegation, raised his right hand to show it was empty. “In the name of Allah, the Compassionate, the Merciful, I and my men come in peace,” he called in Arabic. To be sure the guards understood, he repeated himself in Greek.

The precaution paid off. The guards lowered their bows. In Greek much worse than Jalal ad-Din’s, one of them asked, ”Why for you come in peace, whitebeard?”

Jalal ad-Din stroked his whiskers. Even without the Bulgar’s mockery, he knew they were white. Not many men who had the right to style themselves as-Stambuli, the Constantinopolitan, still lived. More than fifty years had passed since the army of Suleiman and Maslama had taken Constantinople and put an end to the Roman Empire. Then Jalal ad-Din’s beard had not been white. Then he could hardly raise a beard at all.

He spoke in Greek again: “My master the Caliph Abd ar-Rahman asked last year if your Khan Telerikh would care to learn more of Islam, of submission to the one God. This past spring Telerikh sent word that he would. We are the embassy sent to instruct him.”