This is probably a stupid question but I actually never ran into this quest until a couple days ago and I gotta admit it's one of my favorite quests so far. I'm just wondering if it's from a mod or if it's in vanilla Oblivion. It seems so unlike any other Oblivion quest that I keep thinking it's part of a mod... but I haven't downloaded any quest mods.
Little info on the quest if you don't remember the name:
You find a note in the ranger camp west of Kvatch which leads you on a hunt for a wood elf named Eregor, along the way you learn that it's part of a much more sinister plot and also find some very unique armor you cannot wear until you retrieve the Heart of the Wild.