I forget who I got this quest from, but it involves quite a few folks. I believe I picked it up in Connla. It also involves NPCs by the Parth farm, (near DL) and a trip into the Cliffs of Moher to kill Tidal Sheeries, cliff spearmen, and back to get an amadan touched. AFter that, you have to wait until nighttime to kill Amadan Dubh himself.
I'll post quest rewards when I get it.