Beatrice Elvery: Fionn and Áillen (1913);
illustration for Violet Russell’s Heroes of the Dawn (source)

In Irish mythology, Áillen the Burner came forth every Samhain from Mag Mell, the underworld, to burn the scared site of Tara to the ground with his fiery breath after lulling the inhabitants to sleep with sweet music. One year, the great hero Fionn mac Cumhaill breathes in poison from his spear to keep himself awake and kills Áillen, this becoming the leader of all the tribes of Ireland:

Fionn’s eye was the eye of a wild creature that spies on darkness and moves there wittingly. He saw, then, not a thing but a movement; something that was darker than the darkness it loomed on; not a being but a presence, and, as it were, impending pressure. And in a little he heard the deliberate pace of that great being.

Fionn bent to his spear and unloosed its coverings.

Then from the darkness there came another sound; a low, sweet sound; thrillingly joyous, thrillingly low; so low the ear could scarcely note it, so sweet the ear wished to catch nothing else and would strive to hear it rather than all sounds that may be heard by man: the music of another world! the unearthly, dear melody of the Shi’! So sweet it was that the sense strained to it, and having reached must follow drowsily in its wake, and would merge in it, and could not return again to its own place until that strange harmony was finished and the ear restored to freedom.

But Fionn had taken the covering from his spear, and with his brow pressed close to it he kept his mind and all his senses engaged on that sizzling, murderous point.

The music ceased and Aillen hissed a fierce blue flame from his mouth, and it was as though he hissed lightning.

Here it would seem that Fionn used magic, for spreading out his fringed mantle he caught the flame. Rather he stopped it, for it slid from the mantle and sped down into the earth to the depth of twenty-six spans; from which that slope is still called the Glen of the Mantle, and the rise on which Aillen stood is known as the Ard of Fire.

One can imagine the surprise of Aillen mac Midna, seeing his fire caught and quenched by an invisible hand. And one can imagine that at this check he might be frightened, for who would be more terrified than a magician who sees his magic fail, and who, knowing of power, will guess at powers of which he has no conception and may well dread.

Everything had been done by him as it should be done. His pipe had been played and his timpan, all who heard that music should be asleep, and yet his fire was caught in full course and was quenched.

Aillen, with all the terrific strength of which he was master, blew again, and the great jet of blue flame came roaring and whistling from him and was caught and disappeared.

Panic swirled into the man from Faery; he turned from that terrible spot and fled, not knowing what might be behind, but dreading it as he had never before dreaded anything, and the unknown pursued him; that terrible defence became offence and hung to his heel as a wolf pads by the flank of a bull.

And Aillen was not in his own world! He was in the world of men, where movement is not easy and the very air a burden. In his own sphere, in his own element, he might have outrun Fionn, but this was Fionn’s world, Fionn’s element, and the flying god was not gross enough to outstrip him. Yet what a race he gave, for it was but at the entrance to his own Shi’ that the pursuer got close enough. Fionn put a finger into the thong of the great spear, and at that cast night fell on Aillen mac Midna. His eyes went black, his mind whirled and ceased, there came nothingness where he had been, and as the Birgha whistled into his shoulder-blades he withered away, he tumbled emptily and was dead. Fionn took his lovely head from its shoulders and went back through the night to Tara. (source)

Samhain (pronounced SAH-win), of course, is the original Halloween, the ancient Gaelic festival that marks the end of the harvest season and the beginning of winter.