DISCLAIMER: Your Steps and Tasks may be different
Ula mentions that the guards and sentinels are hunting down a certain
Stalker. She asks if you would be willing to assist in a mildly nefarious deed. Upon accepting, she instructs you to speak with a Lurikeen tracker, and attempt to trick him into giving you a note intended for someone else. She then tells you that, once you have the letter, you should deliver it to someone named Achaius, located either
in Tir na mbeo or Ardee.
The tracker is due West, directly across the road; he is wearing red armor, and is named simply "Tracker". Upon speaking with him, he tells you that you look like a Stalker; he asks if you are [here to aid] or if you are [a Stalker]. Choose [here to aid]; choosing [a Stalker] will fail the quest and requires starting over. He gives you a letter to deliver to a guard in green armor, located at the guard post near Tir na mbeo; DO NOT do this, as the quest will fail.
The quest info tells you to deliver it to someone in Howth or Ardagh. Achaius is, in fact, a wandering weapons merchant; he travels between Mag Mell (you'd think the tracker would notice... hard to find good help...) and Ardee. He never reaches Mag Mell, but stops short and heads back North. Deliver it to him for your reward.
You trick the tracker into giving you the letter, and then you give it to someone else.
If you got the quest in the south, you give it to Twm, who runs off because he is being hunted. He's the LARGE guy outside the round building with the two lovers in ARDAUGH.
If you got the quest in the north, you give it Achius, who can be found hiding (ok, standing, but he's a lurikeen) out on the outskirts of TNBeo near the horse seller. Achius is actually in one of the corners of the Tavern in Ardee, outside. As soon as I gave him the letter, he started sprinting towards Mag Mell.