One day as Finn and his companions and dogs were returning from the chase to their Dún on the Hill of Allen, a beautiful fawn started up on their path and the chase swept after her, she taking the way which led to their home. Soon, all the pursuers were left far behind save only Finn himself and his two hounds Bran and Sceolaun. Now these hounds were of strange breed, for Tyren, sister to Murna, the mother of Finn, had been changed into a hound by the enchantment of a woman of the Fairy Folk, who loved Tyren's husband Ullan; and the two hounds of Finn were the children of Tyren, born to her in that shape. Of all hounds in Ireland they were the best, and Finn loved them much, so that it was said he wept but twice in his life, and once was for the death of Bran.

At last, as the chase went on down a valley side, Finn saw the fawn stop and lie down, while the two hounds began to play round her and to lick her face and limbs. So, he gave commandment that none should hurt her, and she followed them to the Dún of Allen, playing with the hounds as she went.

The same night Finn awoke and saw standing by his bed the fairest woman his eyes had ever beheld.

"I am Saba, O Finn," she said, "and I was the fawn ye chased to-day. Because I would not give my love to the Druid of the Fairy Folk, who is named the Dark, he put that shape upon me by his sorceries, and I have borne it these three years. But a slave of his, pitying me, once revealed to me that if I could win to thy great Dún of Allen, O Finn, I should be safe from all enchantments and my natural shape would come to me again. But I feared to be torn in pieces by thy dogs, or wounded by thy hunters, till at last I let myself be overtaken by thee alone and by Bran and Sceolaun, who have the nature of man and would do me no hurt." "Have no fear, maiden," said Finn, "we the Fianna, are free and our guest-friends are free; there is none who shall put compulsion on you here."

So Saba dwelt with Finn, and he made her his wife; and so deep was his love for her that neither the battle nor the chase had any delight for him, and for months he never left her side. She also loved him as deeply, and their joy in each other was like that of the Immortals in the Land of Youth. But at last word came to Finn that the warships of the Northmen were in the bay of Dublin, and he summoned his heroes to the fight, "for," said he to Saba, "the men of Erinn give us tribute and hospitality to defend them from the foreigner, and it were shame to take it from them and not to give that to which we, on our side, are pledged." And he called to mind that great saying of Goll mac Morna when they were once sore bested by a mighty host—"a man," said Goll, "lives after his life but not after his honour."

Seven days was Finn absent, and he drove the Northmen from the shores of Erinn. But on the eighth day he returned, and when he entered his Dún he saw trouble in the eyes of his men and of their fair womenfolk, and Saba was not on the rampart expecting his return. So, he bade them tell him what had chanced, and they said—

"Whilst thou, our father and lord, wert afar off smiting the foreigner, and Saba looking ever down the pass for thy return, we saw one day as it were the likeness of thee approaching, and Bran and Sceolaun at thy heels. And we seemed also to hear the notes of the Fian hunting call blown on the wind. Then Saba hastened to the great gate, and we could not stay her, so eager was she to rush to the phantom. But when she came near, she halted and gave a loud and bitter cry, and the shape of thee smote her with a hazel wand, and lo, there was no woman there anymore, but a deer. Then those hounds chased it, and ever as it strove to reach again the gate of the Dún they turned it back. We all now seized what arms we could and ran out to drive away the enchanter, but when we reached the place there was nothing to be seen, only still we heard the rushing of flying feet and the baying of dogs, and one thought it came from here, and another from there, till at last the uproar died away and all was still. What we could do, O Finn, we did; Saba is gone."

Finn then struck his hand on his breast but spoke no word, and he went to his own chamber. No man saw him for the rest of that day, nor for the day after. Then he came forth, and ordered the matters of the Fianna as of old, but for seven years thereafter he went searching for Saba through every remote glen and dark forest and cavern of Ireland, and he would take no hounds with him save Bran and Sceolaun. But at last he renounced all hope of finding her again, and went hunting as of old. One day as he was following the chase on Ben Gulban in Sligo, he heard the musical bay of the dogs change of a sudden to a fierce growling and yelping as though they were in combat with some beast, and running hastily up he and his men beheld, under a great tree, a naked boy with long hair, and around him the hounds struggling to seize him, but Bran and Sceolaun fighting with them and keeping them off. And the lad was tall and shapely, and as the heroes gathered round he gazed undauntedly on them, never heeding the rout of dogs at his feet. The Fians beat off the dogs and brought the lad home with them, and Finn was very silent and continually searched the lad's countenance with his eyes. In time, the use of speech came to him, and the story that he told was this:—

He had known no father, and no mother save a gentle hind with whom he lived in a most green and pleasant valley shut in on every side by towering cliffs that could not be scaled, or by deep chasms in the earth. In the summer, he lived on fruits and such-like, and in the winter, store of provisions was laid for him in a cave. And there came to them sometimes a tall dark-visaged man, who spoke to his mother, now tenderly, and now in loud menace, but she always shrunk away in fear, and the man departed in anger. At last there came a day when the Dark Man spoke very long with his mother in all tones of entreaty and of tenderness and of rage, but she would still keep aloof and give no sign save of fear and abhorrence. Then at length the Dark Man drew near and smote her with a hazel wand; and with that he turned and went his way, but she, this time, followed him, still looking back at her son and piteously complaining. And he, when he strove to follow, found himself unable to move a limb; and crying out with rage and desolation he fell to the earth and his senses left him. When he came to himself he was on the mountain side, on Ben Gulban, where he remained some days, searching for that green and hidden valley, which he never found again. And after a while the dogs found him; but of the hind his mother and of the Dark Druid, there is no man knows the end.

Finn called his name Oisín, and he became a warrior of fame, but far more famous for the songs and tales that he made; so that of all things to this day that are told of the Fianna of Erinn, men are wont to say, "So sang the bard, Oisín, son of Finn."