He peered tensely at the other musicians. Then he took in a breath and began to sing. The ancient, wordless chant echoed in the darkness, each note husky but true. He caught Valentan’s eye and at his signal, Valentan joined the round. The two voices wound around each other, Valentan’s ringing tenor against Khassian’s baritone. And now the Priests had begun to understand the musical sense of it – they added their voices. Khassian nodded to Azare and he took counter-tenor, adding a third part to the round.

Orial was watching Amaru, her whole body taut, waiting to enter with the treble.

Khassian brought her in with a movement of the hand and her voice became a filament of sound snaking its way through the others, thin, high and pure.

Each part of the round wove into the complex spiral, a growing web of music that spun upwards until the whole hall vibrated.

The complexity of the polyphony generated from the single line of chant melody astounded Khassian. Its exquisite dissonances and resolutions made him want to weep – yet he knew he must keep singing, he must not lose the thread or the whole structure would unravel.

The floor beneath their feet had begun to vibrate in sympathy with the pulsations of the music.

And suddenly Khassian sensed that their voices had been joined by…

Others.

Now he could hear the rustling of many voices, intricate as the tremble of breeze-rippled windchimes, the buzzing of silver-winged bees.

A softspun light seemed to shimmer in the gloom; Khassian narrowed his eyes.

Orial was surrounded.

A phosphorescent glimmer lit the darkness of the Undercity with the eldritch light of marsh-fire.

Slowly the human singers fell silent, awed.

A wreathing circle of translucent, pulsing lights filled the chamber. From time to time a firebright thread of sound would coruscate outwards from the spinning circle. Dizzied, Khassian blinked.

They had come: a host of Eä-Endil, the Winged Ones.

It seemed the vibrations of light and sound mingled until Khassian could no longer distinguish one from the other; his senses were confused; he was hearing the colours, tasting the music. Green notes, acid-sharp, pierced his brain. Then a long, low, sustained pitch, rich as a gilded shaft of autumn sunlight. Now grey, crystalline drops of sound, cold as a spatter of winter rain…

Stones began to shift, ancient mechanisms, older than recorded time, creaking and groaning as the circular plinth on the floor on which Orial stood, slowly swung around. High above, a crack opened in the roof as daylight pierced the darkness, a shaft lighting up the gaping hole.

Steam rose hissing from the gulf below, and with it a spray of hot spring waters.

‘The springs! The springs!’ cried the Priestess.

The Priests fell to their knees. Others followed.

But Khassian still stood, staring transfixed at Orial.

Her pale face was suffused with an iridescent spectrum of light: translucent violet, rose, gold, glimmered in her hair, sapphire and emerald radiated from her eyes.