This quest unlocks after completing "A Man They Call the Sage". To start it, head to the southern part of Havana, where you'll find Stede Bonnet sitting at a table and sipping a drink. Sit down next to him - as you talk, time will pass and evening will fall.
Disappointed with the size of his reward, Edward decides to infiltrate Torres's compound and rescue the man called the Sage.
Hint:
You can enter the estate grounds through a gap in the fence right next to you. Right after passing through, crouch and hide in the tall grass so you don't get spotted by one of the guards guarding the area.
Right after entering the estate grounds, you'll receive further hints.
Hints:
Your next task will be to make your way to the opposite side of this part of the estate grounds. Though you can handle this however you see fit, staying to the left side along the estate walls is one of the simpler options. Start silently eliminating the guards one by one. Be careful not to get spotted by the guards who walk around and patrol the area - and watch out for the guard stationed on the watchtower. To make locating nearby enemies easier, use Eagle Vision and tag the guards in your surroundings. Whistling will also prove to be an invaluable help - use it to lure nearby guards into the tall grass and take them down out of sight of other guards.
Once you reach the opposite side of the area, start moving north still along the walls. Make sure not to run into the guard patrolling the area around one of the buildings.
At some point you'll come across a low wall with crates stacked beneath it. Climb over to the other side.
Eavesdrop on the conversation between two guards to get your next hint.
Hint:
Using the trunk of the leaning tree, make your way onto the villa grounds and climb onto its roof.
From the roof, you should see the Warden drilling a group of soldiers - he's the one with the key. After a moment, everyone will disperse, and the Warden will start patrolling the northeastern part of the villa.
Hint:
From the roof, cross over to the opposite side of the villa - the one with the viewpoint - and take out the two guards there.
Using the opportunity, synchronize the viewpoint and wait until the Warden is directly below you, then perform an Air Assassination. Retrieve the key - Havana Prison Key - from his corpse.
The prison is located on the west side of the villa. Head over there while watching out for the guard patrolling this area - hop over the low wall onto the grounds surrounding the prison and approach the prison door to open it. This will trigger a cutscene where you get captured - which ends this mission and automatically starts the next one - The Treasure Fleet.
