The men came pouring in at the dark mouth of the adit like bees through a hive door. More torches blazed, and the dark slung back. The floor filled with coloured cloaks and the glint of weapons and the flash of jewels. Eyes showed liquid as they looked around them in awe. Their breath steamed on the cold air. There was a rustle and mutter as of folk in a holy place, but no one spoke aloud.

I lifted a hand to beckon the King, and he came forward and stood with me at the edge of the pool. I pointed downwards. Below the surface something—a rock, perhaps—glimmered faintly, shaped like a dragon. I began to speak slowly, as it were testing the air between us. My words fell clear and leaden, like drops of water on rock.

“This is the magic, King Vortigern, that lies beneath your tower. This is why your walls cracked as fast as they could build them. Which of your soothsayers could have showed you what I show you now?”

His two torchbearers had moved forward with him; the others still hung back. Light grew, wavering from the walls, as they advanced. The streams of sliding water caught the light and flowed down to meet their reflections, so that fire seemed to rise through the pool like bubbles in sparkling wine to burst at the surface. Everywhere, as the torches moved, water glittered and sparked, jets and splashes of light breaking and leaping and coalescing across the still surface till the lake was liquid fire, and down the walls the lightfalls ran and glittered like crystals; like the crystal cave come alive and moving and turning round me; like the starred globe of midnight whirling and flashing.

I took my breath in painfully, and spoke again. “If you could drain this pool, King Vortigern, to find what lay beneath it—”

I stopped. The light had changed. Nobody had moved, and the air was still, but the torchlight wavered as men’s hands shook. I could no longer see the King: the flames ran between us. Shadows fled across the streams and staircases of fire, and the cave was full of eyes and wings and hammering hoofs and the scarlet rush of a great dragon stooping on his prey . . .