Nature of the Beast

Background
The Dalish Elves are being destroyed by a virulent disease which is turning them all into werewolves. The clan keeper, Zathrian, asks for your assistance in ridding them of the curse. He requests that you find Witherfang and remove his heart to end the curse destroying his people. You need to investigate the Brecilian Forest to see if you can find more information to end the curse.

Walkthrough
Zathrian sends your party into the forest to find Witherfang and remove his heart to end the curse destroying his people. Before you leave the Dalish camp, it is possible to pick up four side quests -- see the Sidequests section below for more details.

The Brecilian Forest has two sections (West Brecilian and East Brecilian), each of which should be explored completely. You will also come across tombstones which can be activated as part of The Mage's Treasure quest -- the only way to get a full set of Juggernaut Armor in the game.

As you travel through the first section of the forest (West Brecilian), you will fight a lot of werewolves. Eventually you will reach a waterfall with three paths and three werewolves standing within it. This is the first encounter with Swiftrunner, a werewolf who appears to be in charge. He speaks to you; with enough persuasiveness, this encounter does not need to end in battle. After either a peaceful or a violent resolution to the encounter, The Warden can continue into the woods.

In the following area lies a fallen hunter, and The Warden may choose to either let the hunter return to camp or to kill him (Wounded in the Forest quest).

Before leaving the first section of the forest and crossing into the East Brecilian Forest, look for the large tree fallen across the water; the tree contains the Ironbark necessary for the Rare Ironbark quest.

The second area of the forest once again has Werewolves and Wild Sylvan as random encounters. On one of the paths, the Lost to the Curse quest can be continued by speaking to the werewolf lying there. Note: Lost to the Curse can be triggered before you leave the Brecilian Forest by speaking to Danyla's husband.

A section of the forest is protected by an impassable barrier. In order to continue the quest, a way to remove the barrier must be found. At this point, you will be required to explore both sections of the Forest thoroughly in order to find the Grand Oak (in the West Brecilian Forest)  and the Mad Hermit  (in the East Brecilian Forest).

Note: Near the Grand Oak is a campsite. Make sure to save before going near it -- it leads to a possibly fatal encounter. Examining any of the campsite items (tent, fire, sleeping bags) will cause several dialogue options to show up; failing to resist the temptation leads to the party falling asleep and possibly being defeated without a fight. (This can vary; see the Talk page for more details.) In order to ensure survival, attempt to leave after examining only one of the items; a Shade will appear. After the Shade is defeated, the campsite will change, and several chests and corpses to be looted will appear. In the chest under the tree are the Dalish Gloves gift for Zevran.

The answers you give to the various dialogue options seem to affect which of the current party members will be available to help in the battle. (More confirmation is needed for this section.)

Getting through the forest barrier
There are two options available. You will encounter the Grand Oak, who will give you a branch to help you cross the barrier if you retrieve his acorn. His acorn is being held by the Mad Hermit, who wants to keep the acorn.

When siding with the Grand Oak (that is, retrieving its acorn), you may choose to either kill the Hermit or to trade either money, a book, a Silver Ring, or Werewolf Pelts for it. To side with the Hermit, simply attack the Grand Oak.

Note that stealing from the Hermit's tree stump will result in him turning hostile, forcing you to kill him to retrieve the acorn from him.

Upon passing through the barrier, The Warden will once again encounter Swiftrunner. It is impossible to avoid the battle, despite the persuasion options. After the battle is completed, Witherfang appears and the rest of the werewolves scatter. It is now possible to access the Temple Ruins.

Temple Ruins
There is little to do here other than to press on. The werewolves have locked the main door to their lair, leaving The Warden no choice but to take the long way. One of the rooms in the temple contains an altar room, which although listed as a quest unto itself (The Elven Ritual) it is also a necessary part of The Mage's Treasure quest. A Black Vial is found in one of the other rooms of the ruins. Finally, there is a broken altar and Phylactery which can be used to unlock the Arcane Warrior specialization. The entrance to the werewolves' lair is a pool of water, which the Party must to dive into.

Werewolves' Lair
Upon entering the lair, The Warden is met by Shadow Werewolves. They are generally tougher than standard werewolves, will first be encountered in a room littered with traps. Having a rogue disable the traps makes the battle easier. When the main lair is finally reached, there is an opportunity to parlay with the Lady of the Forest. Accepting this opportunity allows The Warden to make a further decision as to the outcome of the quest.

Your choice
The Lady of the Forest will make you aware that the curse began with Zathrian, when he cursed human settlers who murdered his son and raped his daughter. The current werewolves are not, however, those same werewolves, but the poor souls who wandered into the forest and were caught up by the curse. The Lady of the Forest wishes for you to bring Zathrian to the chamber so they may talk. With a high enough persuasion, the Lady of the Forest can alternatively be convinced that the best course of action is to kill all the elves.

Killing the elves and siding with the werewolves results in negative approval from many of the companions (including those who may not yet have been recruited). Any character with a high moral ground will not approve of this choice. Morrigan, however, thinks it's a wonderful idea.

Bringing Zathrian to talk to Witherfang will open the option to have Zathrian and the Lady of the Forest jointly end the curse by sacrificing their lives. Zathrian will not willingly end the curse, and must first be engaged in battle before he is willing to go through with that course of action.

If you bring Zathrian to talk to Witherfang then the werewolves attack first, you have to help Zathrian kill all the werewolves and Witherfang. After that you can just leave with Zathrian or ask him if Lanaya knows how to the cure the curse. He will say "of course," at which point he is no longer useful. The Warden may choose to kill him, though it's not an easy battle.

Result
Once the curse has been lifted, not only are the ailing Dalish cured (if you did not kill them) but the werewolves again become human and immediately leave the ruin. If you sided with the elves, Lanaya (Zathrian's second) will agree to send troops to assist you in fighting the blight. You are now free to explore the Forest to complete the Mage's Treasure Quest. The Mad Hermit's camp is now inhabited by bandits and it is likely that the area beyond the forest barrier is now inhabited by darkspawn. Expect most if not all of these darkspawn to be of the 'Alpha' variety, making this a tough battle if you're unprepared.

If you decided to attack the Elves and side with the Werewolves, you will have Werewolves march to war with you at endgame rather than Elves.

Sidequests
There are four sidequests accessible in the Dalish Camp once Nature of the Beast has been started. The ones marked with * resolve themselves without player action if they are not completed before Nature of the Beast has been finished.
 * Cammen's Lament (This quest will end immediately on your return to the Dalish camp if you only return to Cammen after ending the curse.)
 * Elora's Halla (This quest remains available well after the completion of Nature of the Beast.)
 * Lost to the Curse (If you speak to Danyla's husband prior to entering the Brecilian Forest, this quest is open until you locate Danyla.)
 * Rare Ironbark (This quest is available until you complete the Nature of the Beast quest, as with Cammen's quest, once the werewolves are gone, everyone is free to enter the forest on their own.)