One day Mongan and Duv Laca were playing chess in their palace. Mongan had just made a move of skill, and he looked up from the board to see if Duv Laca seemed as discontented as she had a right to be. He saw then over Duv Laca's shoulder a little black-faced, tufty-headed cleric leaning against the door-post inside the room.
"What are you doing there?" said Mongan.
"What are you doing there yourself?" said the little black-faced cleric.
"Indeed, I have a right to be in my own house," said Mongan.
"Indeed I do not agree with you," said the cleric.
"Where ought I be, then?" said Mongan.
"You ought to be at Dun Fiathac avenging the murder of your father," replied the cleric, "and you ought to be ashamed of yourself for not having done it long ago. You can play chess with your wife when you have won the right to leisure."
"But how can I kill my wife's father?" Mongan exclaimed. "By starting about it at once," said the cleric. "Here is a way of talking!" said Mongan.
"I know," the cleric continued, "that Duv Laca will not agree with a word I say on this subject, and that she will try to prevent you from doing what you have a right to do, for that is a wife's business, but a man's business is to do what I have just told you; so come with me now and do not wait to think about it, and do not wait to play any more chess. Fiachna Duv has only a small force with him at this moment, and we can burn his palace as he burned your father's palace, and kill himself as he killed your father, and crown you King of Ulster rightfully the way he crowned himself wrongfully as a king."
"I begin to think that you own a lucky tongue, my black-faced friend," said Mongan, "and I will go with you."
He collected his forces then, and he burned Fiachna Duv's fortress, and he killed Fiachna Duv, and he was crowned King of Ulster.
Then for the first time he felt secure and at liberty to play chess. But he did not know until afterwards that the black-faced, tufty-headed person was his father Mananna'n, although that was the fact.
There are some who say, however, that Fiachna the Black was killed in the year 624 by the lord of the Scot's Dal Riada, Condad Cerr, at the battle of Ard Carainn; but the people who say this do not know what they are talking about, and they do not care greatly what it is they say.