The sudden fireball sent the workers into a panic. When I uncovered my eyes I saw that some had been badly burned. Others, their loincloths ablaze, were scrambling for blankets to smother the flames.

That was the end of Anubion. The master of the lighthouse had become one with the beacon.

I blinked and looked about, then drew back just as Isidorus rushed past me, quickly followed by Nikanor. Neither of them took any notice of me.

I stood for a long moment, stunned, then hurried down the steps after them.

I emerged on the lower landing, coughing and gasping for breath, eagerly drawing the cool sea breeze into my scalded lungs. The panoramic view of Alexandria and the sea, so enthralling before, was now disorienting and bizarre. I staggered from a sudden attack of vertigo, and watched an unearthly scene play out before me.

Antipater was still on the landing. Isidorus had joined him. They stood with their backs against the parapet and the sea, expressions of shock on their faces.

Nikanor was nearby. At his feet lay a blazing torch. In both hands he held what appeared to be a heavy clay vessel. While I watched, he slung the contents toward Antipater and Isidorus, dousing them with a clear liquid. From the overpowering smell, I realized it was the substance called naphtha.

Nikanor threw the vessel aside and picked up the torch.

My heart leaped to my throat. I rushed toward Nikanor, but he saw me, swung his left arm, and struck me across the face. I reeled to one side and fell.

Before I could make another move, Nikanor threw the torch toward the cowering figures of Antipater and Isidorus.

Antipater was closest to me. I sprang to my feet and leaped toward him. If we had tumbled only a little to one side, Isidorus might have been knocked to the ground and saved as well. But we only brushed him as we fell, and as we struck the hard stone floor there was a burst of flame behind me, followed by a bloodcurdling scream.

“Isidorus!” cried Antipater. I rolled away from him and looked up to witness the final act of the gruesome spectacle.

Like a man made of flames, Isidorus rushed toward his assailant. Even Nikanor was appalled by what he had done. He stood transfixed. Before he could retreat, Isidorus embraced him. Was it a vengeful act? I think Isidorus acted purely by reflex, grasping whatever was closest to him.

Joined by the flames, the two of them performed a hideous dance, traipsing and whirling this way and that, until they collided with the parapet. Flailing in desperation, the madman scrambled to climb over it. Isidorus clung to him. Together they went tumbling over the stone wall.

I rushed to the parapet and watched them descend. Down they plummeted, trailing flames like Phaëton when he wrecked the chariot of the sun. They struck a Triton on the lower parapet with a glancing blow that broke them apart and sent them spinning separately into space, away from the Pharos and over the open sea. The dwindling comets ended in two tiny white splashes, followed an instant later by the sound of two minuscule concussions. Then the sparkling green waves closed over the foam, as if nothing had happened.

Behind me I heard a groan. Antipater had risen to his feet. He looked confused and unsteady. I was a bit shaky myself, as I discovered when I stepped toward him. My legs trembled liked reeds in the wind.

“They fell? You saw them?” he said. Had I not been holding his arm, I think he would have fallen. I almost went down with him. His clothing reeked of naphtha.

“Into the sea,” I said. “But you, Teacher—are you all right?”

“A bit bruised. Nothing broken. Where’s Anubion?”

“Nikanor threw him into the furnace. There’s nothing left of him.”

Antipater looked aghast, then gave a start. “How do you know that man’s name?”

I sighed. “I know a great deal more than that. I saw Nikanor in the street yesterday and recognized him. I followed him. I know what he was up to, in Olympia and here in Alexandria—spying for Mithridates. So was Anubion. So was Isidorus—and you!”

Antipater drew a sharp breath. His eyes darted this way and that.

“Teacher, why did you deceive me?”

He bit his lip. At last he looked me in the eye. “It was for your own good, Gordianus. Had you known, there were times you might have been in great danger.”

“Are you saying I wasn’t in danger, because I didn’t know? That’s no answer, Teacher!”

“Do you regret coming on our journey, Gordianus? Do you wish you’d never left Rome, never seen the Wonders?”

“That’s not an answer, either. You deceived me. I still don’t know what you were up to, in all the places we’ve been—I can only guess. It’s not a question of whether or not you put me in danger. I was tricked. Tricked into aiding and abetting a spy in the service of an enemy of Rome!”

“Rome is not at war with Mithridates—”

“Not yet!” I shook my head, hardly able to look at him. “At the Great Pyramid, do you remember what you called me? ‘A solver of riddles, like your father.’ You said I had a special ability, a gift from the gods—”

“And so you do, Gordianus.”

“Yet all the time, I didn’t see the riddle right in front of me! What a fool you must think me. Pouring praise in my ear, but secretly despising me.”

“No, Gordianus. That’s not true.”

“Tell me one thing: how much did my father know?”

“About my mission? Nothing.”

“Are you saying you fooled him, as well?”

“I convinced him that I wanted to disappear without a trace, for reasons of my own.”

“And he believed you?”

“It’s not such a far-fetched idea. Beyond a certain age, many men harbor such a fantasy—including your father, I imagine. You wouldn’t understand, Gordianus.”

“Because I’m too young?”

“Exactly. The world is not as simple as you think. Did I deceive you? Yes. As for your father, he had his own unspoken reasons for sending you away—he knew that Rome and her Italian allies were on the brink of war and he wanted you well out of it. So he took the opportunity I offered, and didn’t question me as closely as he might have. That doesn’t make him a fool, only a caring father. As for the choices I’ve made—I have no regrets. Friendship matters, Gordianus, but there are things in this world that matter more. Rome must be stopped. Mithridates offers the only hope. If you had to be kept in the dark, what of it? In the meantime, you went on a journey such as most men can only dream of. You followed your aspirations, Gordianus, and I followed mine.”

I shook my head. I searched for words to rebut him. Suddenly he pushed me away.

“Step back, Gordianus,” he whispered. “Get away from me!”

I wondered at this abrupt change, until I heard the sounds of footsteps coming from the tower. At the same time, the Tritons on the lower parapet began to blare discordant notes.

“I’ll think of some way to explain my presence here, and some explanation for what happened,” he whispered. “But for you, it may not be so easy. Go now! Make your way down the tower and back to the mainland.”

“But how can I—”

“They’ll think you’re a worker. Hurry!”

A group of soldiers poured onto the landing, drawing their swords as they did so. They hardly noticed me. Wearing the green tunic, I appeared to be just another worker, and quite a young one at that. Their attention was drawn to Antipater. Our eyes met a final time, and then he was hidden from sight, encircled by the guards.

One of them began loudly to question him. “What happened here? Who fell? Where is Anubion?”

“It was a terrible thing to witness,” cried Antipater, “the ghastly act of some madman!”

I quietly stepped toward the doorway and into the stairwell leading down. As I descended, trying to keep my face a blank, more armed men passed me coming up the stairs. Still more were ascending by means of the mechanical platform in the central shaft. No one challenged me.