A collection of cantos and one of the legends of Ga'Hoole.
The opening paragraph of the Fire Cycle can be found on page 55 in The Siege:
It was in the time of the endless volcanoes. For years and years in the land known as Beyond the Beyond, flames had scraped the sky, turning clouds the color of glowing embers both day and night. The volcanoes that had been dormant for years had begun to erupt. Ash and dust blew across the land and, although it was thought to be a curse from Great Glaux on high, it was something else. For this was the time when Grank, the first collier, was hatched. This was the time when a few special owls discovered that fire could be tamed.
In The Shattering, Ezylryb encouraged Otulissa to read the third canto in the second book of the Fire Cycle, specifically lines 47-99. The first canto, spread across pages 210 and 211, is as follows:
And in the whisper of last moon's light
The dire wolf, Fengo, traversed the night.
And then another and still another followed him,
Until a pack across the earth did roam
Ever onward to seek a warmer home.
Bereft of hope and gnawed by hunger,
They sought a better place to dwell.
Far from the ice-locked country whence they came,
Far from the coldness that was their hell.
And each time a wolf did ask, "Where will this journey end?"
Fengo, their leader, did reply, "Just beyond the yonder. There!
See those fires that scorch the sky
Beyond the mountains that scrape the air?
See the blackness that bleeds hot coals
And makes the darkness shine with light?
Where fires turn the moon bloodred
These same fires melt snow and ice
And leave the land unlocked, undead.
Beyond the next beyond!" Fengo's howl the air did rend.
The wolves howled in return, "Will this journey never end?"
Yet end it did and in its end a new beginning now was found.
And thus did Fengo and his wolves come to this land beyond beyond.
Beneath the fiery cones they made their den.
In rocks and caves of black mountains
That glittered with shards of volcanic glass
Between the coal fields and fires they came to dwell.
This was their heaven and not their hell.
And with that fire monster they made amends.
Yet in that place beyond beyond
Many others met their ends.
--- The second canto, on page 212, reads:
In the darkness of that same night
Another came in desperate flight
To rescue the prince now called Hoole
Set to end the wars so cruel.
--- The last canto, also on page 212, says:
So bring him back with flames of gold.
Bring him back with burning fire.
For he reads what flames have told,
And his will is Hoole's desire.
He shall not cease his endless flight.
He shall fly on through days and nights.
Though an outcast in despair,
He has a gizzard that is so fair.
He shall return at summer's end,
With a coal in his beak, a shadow king no more,
Tempered wise and brave for war.
Furthermore, in chapter fourteen of The Outcast, Otulissa was studying the fourth canto, also at Ezylryb's behest. Its meaning had long been deemed "obscure and controversial." She believed that the previous visitations by the scroom of Strix Struma had a connection to the Fire Cycle as a whole.
Otulissa formerly thought The Fire Cycle was associated with King Hoole only. After reading through it a number of times, she felt it foretold of "another king yet to come who would rule by the grace of the ember," i.e. Coryn.
Aside from these references, not much else is known about the Fire Cycle.