That evening the Turks rushed the walls, and we watched, singing America the Beautiful and arias from Otello, as the brave Genoese of Giovanni Giustiniani drove them off. Arrows whistled overhead; a few of the Byzantines fired clumsy, inaccurate rifles.

I did the final siege so brilliantly that I wept at my own virtuosity. I gave my people naval battles, hand-to-hand encounters at the walls, ceremonies of prayer in Haghia Sophia. I showed them the Turks slyly hauling their ships overland on wooden rollers from the Bosphorus to the Golden Horn, in order to get around the famous chain-boom, and I showed them the terror of the Byzantines when dawn on April 23 revealed 72 Turkish warships at anchor inside the harbor, and I showed them the gallant defeat of those ships by the Genoese.

We skipped forward through the days of the siege, watching the walls diminishing but remaining unbreached, watching the fortitude of the defenders grow and the determination of the attackers lessen. On May 28 we went by night to Haghia Sophia, to attend the last Christian service ever to be held there. It seemed that all the city was in the cathedral: Emperor Constantine XI and his court, beggars and thieves, merchants, pimps, Roman Catholics from Genoa and Venice, soldiers and sailors, dukes and prelates, and also a good many disguised visitors from the future, more, perhaps, than all the rest combined. We listened to the bells tolling, and to the melancholy Kyrie, and we dropped to our knees, and many, even some of the time-travelers, wept for Byzantium, and when the service ended the lights were dimmed, veiling the glittering mosaics and frescoes.

And then it was May 29, and we saw a world on its last day.

At two in the morning the Turks rushed St. Romanus Gate. Giustiniani was wounded; the fighting was terrible, and I had to keep my people back from it; the rhythmic “Allah! Allah!” grew until it filled the universe with noise, and the defenders panicked and fled, and the Turks burst into the city.

“All is over,” I said. “Emperor Constantine perishes in battle. Thousands flee the city; thousands take refuge behind the barred doors of Haghia Sophia. Look now: the pillaging, the slaughter!” We jumped frantically, vanishing and reappearing, so that we would not be run down by the horsemen galloping joyously through the streets. Probably we startled a good many Turks, but in all that frenzy the miraculous vanishing of a few pilgrims would attract no excitement. For a climax I swept them into May 30, and we watched Sultan Mehmet ride in triumph into Byzantium, flanked by viziers and pashas and janissaries.

“He halts outside Haghia Sophia,” I whispered. “He scoops up dirt, drops it on his turban; it is his act of contrition before Allah, who has given him such a glorious victory. Now he goes in. It would not be safe for us to follow him there. Inside he finds a Turk hacking up the mosaic floor, which he regards as impious; the sultan will strike the man and forbid him to harm the cathedral, and then he will go to the altar and climb upon it and make his Salaam. Haghia Sophia becomes Ayasofya, the mosque. There is no more Byzantium. Come. Now we go down the line.”

Dazed by what they had seen, my six tourists let me adjust their timers. I sounded the note on my pitchpipe, and down the line we went to 2059.

In the Time Service office afterward, the Ohio real-estate man approached me. He stuck out his thumb in the vulgar way that vulgar people do, when they’re offering a tip. “Son,” he said, “I just want to tell you, that was one hell of a job you did! Come on over with me and let me stick this thumb on the input plate and give you a little bit of appreciation, okay?”

“I’m sorry,” I said. “We’re not permitted to accept gratuities.”

“Crap on that, son. Suppose you don’t pay any attention, and I just get some stash thumbed into your account, okay? Let’s say you don’t know a thing about it.”

“I can’t prevent a transfer of funds that I don’t know about,” I said.

“Good deal. By damn, when those Turks came into the city, what a show! What a show!”

When I got next month’s account statement I found he had thumbed a cool thousand into my credit. I didn’t report myself to my superiors. I figured I had earned it, rules or not.

I figured I had also earned the right to spend my layoff at Metaxas’ villa in 1105. No longer a pest, a driveling apprentice, I was a full member of the brotherhood of Time Couriers. And one of the best in the business, in my opinion. I didn’t have to fear that I’d be unwelcome at Metaxas’ place.

Checking the assignment board, I found that Metaxas, like myself, had just finished a tour. That meant he’d be at his villa. I picked up a fresh outfit of Byzantine clothes, requisitioned a pouch of gold bezants, and got ready to jump to 1105.

Then I remembered the Paradox of Discontinuity.

I didn’t know when in 1105 I was supposed to arrive. And I had to allow for Metaxas’ now-time basis up there. In now-time for me it was currently November, 2059. Metaxas had just jumped up the line to some point in 1105 that corresponded, for him, to November of 2059. Suppose that point was in July, 1105. If, not knowing that, I shunted back to — say — March, 1105, the Metaxas I’d find wouldn’t know me at all. I’d be just some uninvited snot barging in on the party. If I jumped to — say — June, 1105, I’d be the young new-comer, not yet a proven quantity, whom Metaxas had just taken out on a training trip. And if I jumped to — say — October, 1105, I’d meet a Metaxas who was three months ahead of me on a now-time basis, and who therefore knew details of my own future. That would be the Paradox of Discontinuity in the other direction, and I wasn’t eager to experience it; it’s dangerous and a little frightening to run into someone who has lived through a period that you haven’t reached yet, and no Time Serviceman enjoys it.

I needed help.

I went to Spiros Protopopolos and said, “Metaxas invited me to visit him during my layoff, but I don’t know when he is.”

Cautiously Protopopolos said, “Why do you think I know? He doesn’t confide in me.”

“I thought he might have left some record with you of his now-time basis.”

“What the hell are you talking about?”

I wondered if I had made some hideous blunder. Bulling ahead, I winked and said, “Youknow where Metaxas is now. And maybe you know when, too. Come on, Proto. I’m in on the story. You don’t need to be cagey with me.”

He went into the next room and consulted Plastiras and Herschel. They must have vouched for me. Protopopolos, returning, whispered in my ear, “August 17, 1105. Say hello for me.”

I thanked him and got on my way.

Metaxas lived in the suburbs, outside the walls of Constantinople. Land was cheap out there in the early twelfth century, thanks to such disturbances as the invasion of the marauding Patzinak barbarians in 1090 and the arrival of the disorderly rabble of Crusaders six years later. The settlers outside the walls had suffered badly then. Many fine estates had gone on the market. Metaxas had bought in 1095, when the landowners were still in shock over their injuries at the hands of the Patzinaks and were starting to worry about the next set of invaders.

He had one advantage denied to the sellers: he had already looked down the line and seen how stable things would be in the years just ahead, under Alexius I Comnenus. He knew that the countryside in which his villa was set would be spared from harm all during the twelfth century.

I crossed into Old Istanbul and cabbed out to the ruins of the city wall, and beyond it for about five kilometers. Naturally, this wasn’t any suburban countryside in now-time, but just a gray sprawling extension of the modern city.