His horse was bucking and becoming difficult to control. If he panicked and fled, it would be all over for Rufus. He tied the reins to a tree branch so he could move more freely, then clutching his knife in one hand, he continued to wield the brand, which had burned right down to a stub, with the other.

Wolves had never been a problem before. It had always been easy to scare them off. Why were these ones so tenacious and aggressive? He thought of the legend about how his ancestors first arrived in Italy, guided by a wolf. But these were different, ravenous beasts with the worst of intentions. He backed up against a big fir tree and felt the lowest branches crackle, dry and brittle against his cloak. The gods had sent him help. He snapped them off and tossed them on what remained of the brand. The flame sparked up thanks to the resin in the wood and he thrust it forward.

The sudden flare repelled the wolves, but drove them back only just beyond the circle of light. The horse was kicking and whinnying and tugging wildly at the reins. If he hadn’t been wearing a bit, he would already have run off. Rufus wondered whether his commander could see this fire as well from the terrace of Lux fidelis. Someone was seeing it for sure, but they would never abandon the base without a good reason.

The duel between hunger and flames was about to end with the fire going out. Rufus then did the last possible thing he could, although it was deeply repugnant to him. He begged the gods of his forefathers to forgive him before he piled all the dry branches which remained around the base of the trunk. The fir tree caught fire and in just minutes had turned into a huge blazing torch. His Celtic soul was horrified by the screams he could hear from the spirit of the great fir racked by the flames, but his Roman soul justified the act because he was following the orders of his superiors.

The wolves fled. Rufus picked up one of the fallen branches that was still burning, mounted his horse and continued on his way, crossing a wide clearing and finally reaching the grey slate slabs of the Via Flaminia Minor.

In Monte Appennino, Lux fidelis, a.d. V Id. Mart., tertia vigilia

The Apennine Mountains, Faithful Light, 11 March, third guard shift, one a.m.

The station commander had just fallen into a deep sleep when a servant shook him awake.

‘What in Hades is going on?’ he demanded.

‘Master, come immediately — you must see this!’

The commander threw a cloak over his shoulders and, dressed as he was, made his way to the upper terrace. It was snowing and the vision that greeted him was like nothing he’d ever seen before. Directly to the south, at a distance that was difficult to assess, and at an altitude that made the scene look as if it was playing out in mid-air, he could see a globe of intense light surrounded by a reddish halo that trailed off in the direction of the wind in a kind of luminescent tail.

‘Ye gods! What is it?’

‘I don’t know, commander,’ replied the sentry. ‘I have no idea. I sent the boy to wake you as soon as it started.’

‘A comet. . with a tail of blood. . powerful gods! Something terrible is about to happen. Comets bring misfortune. This is a cursed night, lads,’ he added. ‘Keep your eyes wide open.’

He pulled the cloak tight, as if warding off any evil influence, then hurried back down the stairs and locked himself in his room.

Outside, on the terrace, the servant could not take his eyes off the strange phenomenon, and it surprised him when the light became much brighter for a few instants and then faded until it was swallowed up by the darkness.

The servant turned towards the sentry. ‘It’s gone,’ he said.

‘Right,’ replied the sentry.

‘What does that mean?’

‘Nothing. It means nothing. The commander said it was a comet. Didn’t you hear him?’

‘What’s a comet?’

‘How am I supposed to know? Go and ask him. And while you’re downstairs get me some hot wine. I’m freezing out here.’

The servant ducked down through the hatch, leaving the sentry alone to keep watch over the night.

Ad flumen secretum, a.d. V Id. Mart., tertia vigilia

The secret river, 11 March, third guard shift, one a.m.

Mustela awoke feeling groggy and numb. He had no idea how long he’d been lying there, curled up in the damp grass. He was completely soaked through. There was no part of his body that didn t hurt and his chest shook with a dry, hacking cough. It was dark and all he could see was the water of the torrent flowing at a short distance. Where was the boat the old man had promised him? He looked around and immediately noticed a clump of trees a little further along the bank. He staggered in that direction. Could those be willows?

A break in the clouds revealed a sliver of moon and for a few seconds Mustela could see that they were indeed, and, sure enough, there was a boat tied to a stake in the river. The dark outline stood out clearly against the silvery moonlit water.

He was close now to the end of his mission. The worst was over, as long as he didn’t pass out first. He touched the bandage on his side and his hand came back sticky. So he hadn’t managed to stop the bleeding. He fastened the bandage tighter, then walked over to the boat and got in. He pushed off from the bank using one of the oars, then rowed his way into the middle of the current.

All he had to do was let the water carry him, so that’s what he did, and little by little, as the river made its way to the plain, the temperature became milder. A light, warm breeze from the south dried him off. The sky behind him was dark and streaked with lightning bolts, but it was slowly growing lighter in front of him. Every now and then, Mustela sunk down to the bottom of the boat and drifted into a light sleep, just for long enough to clear his head.

At the slightest bump his eyes would jerk open and he would take to watching the scenery, the villages and isolated farms gliding past, dark objects standing out against the pale light of dawn. He could hear sounds, but they were largely unintelligible. Once there was someone calling, another time he thought he heard a wail of despair, but for the most part it was just the mournful hiccuping of the screech owls and the insistent, syncopated hooting of other night birds.

It was full daylight and the countryside had begun to come to life when he finally saw it: the Arno!

The torrent he was travelling on flowed into the great Etruscan river that wound lazily down the hillside in great loops, heading towards the plain. The current was becoming much slower, but Mustela was sure that he had been carried many miles downstream.

Although it was hidden by the clouds, he calculated that the sun was high by the time he reached the landing pier at a little river harbour where goods from the mountains were stocked before being sent on to Arezzo, still a considerable distance away. With what little strength he had left, Mustela used the oars to bring him towards the pier and managed to draw up alongside it. The owner of one of the storehouses rented him a mule and gave him a piece of clean fabric so he could change the bandage on his wound, then Mustela continued his journey to the house of the cypresses, hidden inland.

Of all the messengers who had left the Mutatio ad Medias, he had to be the one who had arrived furthest south. Who else could have got as far as he had by travelling downstream on a rushing underground torrent?

Every jolt, at just about every step the mule took on the cobblestoned street, produced a stabbing pain in his side. His muscles, stiff from exertion, numb with cold and cramping with hunger, had long ceased to respond, and tough old Mustela — who’d been through thick and thin in his long life as an informer — could think of nothing other than crawling into a clean bed, in a warm, sheltered place.