I was beside the king and Myrddin in an instant, and saw what had brought them up short. The forest, last seen as a thick line on the far southern horizon, now rose directly before us -a dense growth of hornbeam, elm, and oak standing just across the valley.

Astonished beyond words, I stared at the wood as if never having seen a tree before. There was, so far as I could determine, nothing at all to suggest that the trees I saw before me were not what they appeared: solid and thick and, like all trees everywhere, deeply rooted to their places through years of slow, inexorable growth.

Gazing in disbelief at the dense woodland, I slowly became aware of a strange, unsettling sound. I think the sound had been there from the first, but I noticed it only after the first shock of seeing the trees had passed. Nor was I the only one to hear it.

'What is that?' asked Arthur, his voice low. He half turned his head, but his eyes did not leave the dark wood for a moment. 'It sounds like teeth clicking.'

Truly, it did; it was the sound of many teeth, large and small, gnashing against one another – not fiercely, but softly, almost gently, in a low, gabbled muttering.

Arthur's eyes swept left and right along the stout line of trees for any break in the wood. The line met us as a timber wall, and there was no breach to be seen anywhere along its thick-grown length save one only: directly ahead, a gap opened between the close-grown trees.

The trail we pursued led straight into the heart of that dark wood. What is more, the mist was rising again; it was already filling the valley between us and the wood's edge.

Bedwyr and Cador reined up beside us then. Having observed the forest from their rearward places, they now joined us to learn what the king and his Wise Counsellor made of it. 'Unless it was hidden by mist,' Bedwyr declared, 'I cannot think how it has come to be here otherwise.'

'Perhaps,' Cador suggested, 'like the warriors in your story, Myrddin, we have slept a thousand years, and the wood has grown up around us.'

Bedwyr frowned at Cador's frivolity, and reproached him with an indignant grunt. But Myrddin said, 'In this place, that is as sound an explanation as any other.'

'If that is what passes for reason,' Bedwyr said darkly, 'then folly is king, and madness reigns.'

'A wall before us, a wall behind. There is but one way through,' Arthur said, 'and there is no turning back.'

So saying, he raised his hand and signalled the column to move on. I returned to my place behind Myrddin. 'Well,' I said to Rhys as we urged our horses forward once more, 'we are going in.'

'Was there ever any question?'

'No,' I answered. 'Aliajacta est.'

'What does that mean?' he asked.

The die is cast,' I told him. 'It is something old Caesar once said.'

'Who told you that?'

'My father used to say it – I never knew why. But lately, I begin to think I know what he meant.'

We crossed the valley and entered the wood in silence. No one spoke, and all kept a keen eye for any sign of attack, though many, I noticed, cast a last glance at the sky before the intertwining branches closed overhead. It was like entering a tomb – so close and dark and silent was the unchancy wood. The trail narrowed as it passed among the broad boles of the trees, but rather than ride single file, the men urged their horses together and rode shoulder to shoulder and flank to flank.

Like all the others, I cast a longing glance behind me as we entered the wood and saw the same look of sick apprehension on one face after another. But there was nothing for it. We clutched our weapons more tightly and hunched lower in the saddle as if to escape notice of the tight-crowded trees.

Keeping my eyes on Myrddin and Arthur ahead of me, I remained alert to the sounds around me, but there was little to hear; a thick mat of pine needles cushioned the horses' hooves, and the men made no sound at all. Neither was any birdsong heard – nothing, in fact, but the incessant clicking, and the hush of muffled breath passing into the dank, dark air.

As to the ceaseless clicking and clicking and clicking, after a time I discovered what created that unsettling sound: the wind twitching the bare upper branches. Fitful and gusty, the wind did not penetrate the forest at all, but continually mumbled and fretted overhead, stirring uneasily in the high treetops and making the thin branches quiver. So close were these limbs and so entangled, they chattered against one another in endless motion. Even this, however, did not strike the ear with any vigour, but reached us as a faint muttering falling from high above, sinking down and down into the soft forest floor below.

The forest swallowed everything that came into it – sunlight and wind, and now the Pendragon and his warband. Everyone who conies into a woodland wild feels something of this oppressive enclosing; it is what causes a traveller to skirt the shadows and stay to the trail, proceeding with wary caution. What is more, this uncanny sensation seemed to increase with every step deeper into the wood until it took on an almost suffocating aspect, becoming a thing of towering proximity and ponderous weight.

We came upon a stream – little more than a muddy rivulet dividing the trail – and stopped to water the horses, taking it in turn by twos, and then moving on to allow those behind to get at the water. We rode a fair way farther, whereupon Arthur halted the columns, turned his horse, and sat looking down the long double line of warriors. Without a word, Myrddin rode down the centre, passing between the warriors.

'What do you see, lord?' I asked, turning in the saddle to learn what held his attention.

'It is what I am not seeing that causes me concern,' the king replied, still gazing back along the trail.

The trees along each side and the branches thickly interwoven above made of our trail a shadowy tunnel, like the entry shaft of a cave or mine. The Cymbrogi, riding close to one another, sat their horses, awaiting the call to move on. Owing to the dimness of the light and the narrowness of the trail, I could not see past more than twelve or fifteen riders as I looked down the line. Yet I could discern nothing amiss.

I was about to say as much when Myrddin shouted something and came pounding back along the trail to join us.

'Well?' said the king.

'I cannot see them,' Myrddin replied. 'They should have rejoined us by now.'

Only then did I realize what they were talking about. The fifteen or so pairs that I saw behind us were, indeed, all that remained of the long double column. The others were not lost to the shadows – they were gone completely. Obviously, we had become separated from the rest of the warhost. The warband led by Bedwyr and Cador had vanished.

'Lord, allow me to ride back and find out what has happened,' I volunteered. 'No doubt meet them before I have gone a hundred paces.'

'Very well,' Arthur agreed, 'but take Rhys with you – let him signal us when you have reached them. We will wait for you here.'

I returned to my horse and informed Rhys of the king's command as I swung into the saddle. We passed down the line of warriors and back along the trail. I counted thirteen pair: twenty-six warriors out of fifty, I thought, and wondered what had become of the rest. Could twenty-four mounted warriors simply disappear?

Once past the last of the Cymbrogi, we urged our mounts to speed and raced along the close-grown track. When, after a fair ride, we still caught no sight of the stragglers, I halted. 'We should have seen them by now,' Rhys said as he reined up beside me. 'What could have happened to them?'

'Until we find them, we only waste our breath asking such questions,' I pointed out. In Llyonesse, anything might happen, I thought, but kept the thought to myself.

'Well, what do you suggest, O Head of Wisdom?' Rhys gave me a sour frown.