The twins were born to Fianna, queen of Gleann Fiain in Dun Glas. But unbeknown to her husband, Ceannann mac Ceannann, Fianna was unable to conceive and had sought help from a wise-women, Moragacht. Moragacht struck a bargain with her, promising her twins if she lay down with a selkie, in exchange for one of the twins when they were born. But when the twins arrived (a human and a selkie) and Moragacht came to claim one of them, Fianna denied any knowledge of her, and mac Ceannann turned Moragacht away. From that day onwards, grief and misery struck the family, and mac Ceannann and Fianna were forced to vacate Dun Glas and flee with the twins to an abandoned hilltop fortress. But the loch beast, under Moragacht's control, found them there and killed them all, except the twins, now aged 14, who escaped to the cottage. The witch then seized control of Dun Glas from where she damned all of Gleann Fiain.