Oblivion:Dunbarrow Cove (quest)

Quick Walkthrough
# Install the Thieves Den official plug-in.
# After receiving the message about the great battle of Anvil Bay, travel to Smuggler's Cave underneath Anvil Castle.
# Find your way to Dunbarrow Cove and rid the Cove of the haunted Skeletons.
# Visit Dahlia Rackham of the Clarabella in Anvil Bay to purchase upgrades, including a crew.
# Once all upgrades are purchased the quest is complete.

Detailed Walkthrough
A Great Battle
When you start or load the game, you will receive a message: 
:Centuries ago, a great battle took place in Anvil Bay. In the battle, the legendary pirate Torradan ap Dugal, the captain of the infamous Black Flag, was defeated by the first Count of Anvil. Rumors have been circulating of a hidden underground cavern beneath Castle Anvil. If the rumors are to be believed, then the final resting place of Captain Dugal and his ship have been uncovered. I should investigate these rumors as soon as possible. 

The map will be marked just southeast of Castle Anvil at a location named Smuggler's Cave. If you start a new game with this plugin loaded, the note and quest will be given to you right after you select your class the first time in the tutorial level.

The Secret Cave
Head there and alongside the foundation of Castle Anvil you will see the door to Smuggler's Cave. Enter the cave and go straight; this leads to the door that opens into the inner zone named Dunbarrow Cove. The Red Sabre Pirates that were trapped here years ago have since died of illness and now their skeletons walk the cove, forever damned in anger over their grave misfortune.

Lore of the Red Sabre
You will have to defeat all seven Red Sabre skeletons, including the skeleton of Cap'n Dugal in the Captain's Quarters.  (This can be made quite easy by killing all of the skeletons outside, and then sneaking into the Captain's Quarters for a sneak attack on Cap'n Dugal.  Once you've done so, immediately go back through the door.  For whatever reason, he doesn't follow,(He does follow in the latest edition on Steam) and when you re-enter, he will no longer be aggressive.  This will allow for low level players, particularly with low health and weak weapons, to easily kill him off. Simply perform a sneak attack, leave immediately, and then repeat. He should die without issue.)  In the Captain's Quarters you will also find four volumes of ''Cap'n Dugal's Journal'' which provides the back-story of Cap'n Dugal and the Black Flag.  After you have defeated the undead pirates, you will receive a quest update saying you should see Dahlia Rackham of the Clarabella to hire a crew; the Clarabella is located in Anvil's harbor.

Bugs
Similar to the Deepscorn Hollow bug, it is possible for the player to enter the Smuggler's Cave without going near enough to the map marker to trigger the quest popup. If all of the Red Sabre Skeletons (including Cap'n Dugal) are dead and no update appears, then this has happened. Console players will have to repeat the quest (to avoid a recurrence, fast travel to the Dunbarrow Cove map marker before going into the entrance) but for PC players, enter the following into the console:  setstage DLC06ThievesDen 11 , and the quest should then proceed normally.
 
 
It is possible to get close to the entrance to Smuggler's Cave and the quest marker on the compass redirects you to go inside Anvil and back to the same place in a loop. The local map is the one that shows the marker in the correct spot.

Quest Stages