Location Map:
HERE
Next I will talk about how to go about finding Captain Dreavers. On the location map there will be a mark on it saying "Captain Dreavers", this will bring you to a run down village where level 42 - 43 (3 and 4 dot) Cartheon mobs have taken over. This outpost also had some general quests attached to it that you receive while you are in Haven's Edge.
So in order to kill Captain Dreavers, you will need to spawn him. In order to spawn him, you will need to collect his body parts that drop randomly off of the Cartheon mobs that occupy the village. In total, there are 4 body parts needed: His head, his torso, his legs, and his arms. If you are in a group, have one person collect all 4 parts.

Now, when you have all of the body parts, you will need to go to his grave to spawn him. His grave is located outside of the village (there is a tombstone in the middle of the village that you can click. This is NOT the right grave) to the southeast side. It will be next to a rather large rock, and should be clickable for the person that has all 4 of his body parts.
When you guys are buffed up and ready, have the group standing near the grave, and the puller standing close to the middle of the village. Why? Because once you spawn the Captain, he will spawn in the middle of town. Have the puller, drag him to the rest of the group and start your kill. He will be a level 43 4dot, and look like a green ghost, on a green ghost horse. Kill him and he shall drop an Unmarked Armor piece, as well as some loot.
NOTE: When you spawn dreavers, the body parts used to spawn him will disappear from your inventory. Technically you can spawn him as many times as you like. As long as somebody in your group has the 4 body parts for the turn in, he will spawn.