You can start this quest immediately after completing "The Siege of Charles-Towne" - simply sit on the bench in the tavern in Nassau. Captain Woodes Rogers and Commodore Chamberlaine will arrive in Nassau wanting to parley.
Governor Woodes Rogers arrives to Nassau, offering the King's pardon to all pirates. Edward tails him to discover his ultimate plans.
Hint:
You don't actually have to tail him. Rogers will make his way from the beach to the tavern in Nassau - so you can simply head there and wait for him on the roof of the adjacent building.
Once Rogers reaches the tavern, listen patiently to what he has to say. He will want to speak with several pirates - and then they will all head off toward the fort.
Anne is in the tavern - so just a few steps away from you. You will learn from her about secret documents that you will, of course, decide to look at.
Hint:
Approach the fort walls from the south side. You will find two tents and a small scaffolding here. If you start climbing here - you will be able to reach the very top of the fortress walls. Get onto the scaffolding, go around the corner of the walls, jump across a few trees - and climb up a few wooden platforms.
Once you reach the top of the walls, use eagle vision to check if there is a guard patrolling the wall to your right - and if the coast is clear, move straight ahead (heading left along the walls).
You don't need to worry about the guard you are about to see - he won't turn around. Turn right onto the wooden platform - check if the Brute patrolling the area below is not nearby - and jump down into the bushes growing next to the alarm bell.
The plans you need to steal are lying on the table next to the wooden building on the other side of the courtyard. To pick them up, you must not have aggro.
Wait until the Brute is nowhere nearby - or lure him into the bushes and assassinate him - then loop around the middle wall counterclockwise to approach the two guards standing near the house from behind and double assassinate them.
Next, sneak up behind the soldier standing closest to the house and assassinate him as well.
You can now pick up the document, which will trigger a cutscene. The meeting with the pirates will conclude - leaving them divided on how they should proceed.
Once the cutscene ends, you must leave the fort. You don't need to worry about drawing aggro - you can simply sprint up the stairs to the walls...
and perform a leap of faith into the hay cart below. This quest will end, unlocking the next one - The Gunpowder Plot.
