My recollection is that this is the Dierdre that married the Sons of Usnoth, and were exiled from Ireland to Scotland. I forget whether the sons of Usnoth were killed there or after a return to Ireland. An old Irish tale, about which a song was made. No Lorna Doone here, thoughTune is "Deirdre's Lamentation for the Sons of Usnoth Irish" in O'Farrell's Pocket Companion, II, c 1811. Verses and music in Bunting's 1840 collection.