'It is a foul shame in thee to say that,' said Oscar, 'and I pledge the word of a soldier that unless the heavens fall upon me or the earth opens under my feet, I will not suffer you nor your Fenians to strike him a single blow, and I will take him under my protection, and keep him safe in spite of you all. Therefore, O Diarmid, come down out of the tree, since Fionn will not grant you mercy. 'I will pledge that no evil will come to you to-day.'
So Diarmid rose, and stood upon the topmost bough of the tree, and leapt light and birdlike, by the shafts of his spears, and passed out far beyond Fionn and the Fenians of Erin. And he and Oscar went their way, and no tidings were heard of them till they reached Grania and Angus on the banks of the Boyne.
After Diarmid and Oscar had departed, Fionn ordered a ship to be made ready, and as soon as it was done he marched on board with a thousand of his warriors and set sail for the north of Scotland. When he arrived at the harbour nearest the King's palace, he moored his ship and took the path to the palace, where the King received him kindly, and gave him food and drink. Then Fionn told the King why he was come. 'And truly you should give me a host,' said he, 'for Diarmid it was who slew your father and two brothers and many of your men besides.'
'That is so,' answered the King, 'and I will give you my two sons, with a thousand men to each of them.' Joyful was Fionn to hear this, and he departed with his company, and nothing was known of them till they reached the Boyne, where Fionn challenged Diarmid and Angus to battle.
'What shall I do touching this, O Oscar?' asked Diarmid.
'We will give them battle and slay them all,' answered Oscar.
On the morrow Diarmid and Oscar rose, and put on their armour and went their way to the place of combat, where they bound the rims of their shields together, so that they might not be parted in the fight. Next they proclaimed battle against Fionn, and the Scots said they would land and fight them first. They rushed together, and Diarmid passed under them and through them and over them, as a whale would go through small fish. And all of them fell by Diarmid and Oscar before night came, while they themselves had neither cut nor wound.
When Fionn saw that great slaughter he and his men put out to sea, and sailed to the cave where dwelt an old woman, Fionn's nurse. And he told her his story from the beginning. 'I will go with you,' said she, 'and will practise magic against him.'
They came to the Boyne, and the witch threw magic over Fionn and his Fenians, so that the men of Erin knew not they were there; and that day Diarmid was hunting alone, for he had parted from Oscar the day before. Now the witch knew this, and she flew to where a water-lily leaf lay with a hole in the middle of it, and as the wind lifted the leaf from the surface of the water she cast deadly darts at Diarmid through the hole, and did him great hurt. And every evil that had come upon him was little compared with that evil. Then he felt that unless he could strike her through the hole in the leaf she would slay him on the spot; so he lay down on his back and took his javelin in his hand, and reached her through the hole, and she fell dead.
After that he cut off her head and carried it with him to Angus.