Guild Wars 2 – Hounds and the Hunted

Head out to the Slieve's Waypoint. Just to the North of that you will find the entrance to the instance itself. Just head on inside it to begin the mission proper.

Follow the road in front of you as it winds to the West. At the top

Hero: “Gavin, are you feeling better?”
Gavin: “I am, thanks to you. I have good news. The white stag has been seen in the area recently. If we hurry, we could catch up to it.”
Hero: “That watchtower over there gives me an idea. From the top we can get the lay of the land, possible, a glimpse of our quarry.”
Gavin: “You have a true hunter's instincts, Valiant. That's exactly what we should do. When the stag appears, we shall give chase until it tires. Together, we will harry it – and then, the beast shall be ours!”

Follow Gavin to the base of the tower and take the winding vine upwards. At the top you will find the White Stag. Head back on down then move over to the marked location to the East. As you approach the stag you will need to start dealing with numerous Risen Thrulls. You start with just a pair. After the stag has been alerted to you another pair of Risen Thrulls will appear. All this Risen Thrulls are lvl. 4.

Follow the stag to the South. As you approach it 3 Risen Thrulls will appear and attack you. It will move some then another Risen Thrull will appear. Head over to the East then another pair of Risen Thrulls appear. After that you have plenty of pairs of Thrulls.

Defeat them all and continue to the East after the stag. After it finishes moving then another pair of Risen will appear. The Stag will head off to the East after that bunch. At its next pause there will be a good 4 Risen, including one with a maul.

Head to the North after that to keep on the stag. More Risen await you there. When it turns to the West is when it is truly starting to get tired. Just keep a solid, aggressive approach on all of the Risen. They are trying very hard to kill you. Inside that final group you will find another massive Risen with a maul. Finish out the remaining Risen and approach the stag one more time.

It will gallop off and Gavin will catch it in a net. He turns and talks with the hero:
Gavin: “Excellent work, Valiant. But now I must leave. And I will be taking the white stag with me. You're welcome to come, of course. Your skills as a hunter would be an asset to the Court.”
Hero: “The Nightmare Court? Who are they, and what are you doing? Gavin, the stag must go back to the Grove. Caithe is waiting for us there.”
Gavin: “No, my noble friend. The White stag is coming with me. Once we turn it to the Nightmare, the stag will be a powerful weapon against the Dream. It is a manifestation of hope and faith. In Nightmare, it will be just the opposite – a creature of despair and hatred. Through its power, the Pale Tree will be freed of the chains forged by Ventari's Tablet.”
Hero: “A weapon? Gavin, this is wrong. The White stag is a peaceful creature. You can't turn it into something cruel.”
Gavin: “I can. We can. Come with me. You would be celebrated. Possibly even knighted by the grand Duchess herself!”
Hero: “No Gavin. I'll never join the Nightmare Court.”
Gavin: “Ah, that's a pity. It grieves me greatly to turn predator to pray, Valiant, but I cannot have you interfere. Farewell.”

After Gavin runs away you will be attacked by 3 Nightmare Hounds. All of which are lvl. 4. Break away from the pack and fight them as best suits you. After the trio you have an Alpha Nightmare Hound come after you. He is lvl. 5 and stronger than the rest (or at least tougher).

When the fight is over you will find the exit from the instance and it is time to get over to Caithe. Head to the Grove and drop down to your home instance. There you will find her.

Hero: “Caithe, I need your help. Gavin, the hunter working with me to track the white stag, has betrayed me. I don't understand what he's done. He said something about using the stag as a weapon and that Ventari's tablet was evil. He said he was a member of the Nightmare Court.”
Caithe: “The Nightmare Court? Thorns! You were right to come to me. They believe that Ventari's Tablet had turned the tree away from the original nature of the Dream. They embrace pain and darkness, and they claim that Ventari's lessons have corrupted the Sylvari – and the Pale Tree.”
Hero: Corrupted us? Can't they see that they're the ones who became poisonous?
Caithe: “They believe their own lies. Come, Valiant. We must discover where the court is holding the white stag.”
Hero: “I agree, but how?”
Caithe: “News of such a prize would have spread among the courtiers like wildfire. We will go to Aron's Woodlot, and spy upon the court. They often go there to recruit new courtiers, but we must be subtlew, or they will flee without telling us anything. Meet me there, and we will devise a plan.”