This quest will be unlocked after completing the "Traveling Salesman" quest. To start it, you must speak with James Kidd, who can be found on the roof of the windmill standing near Prins' estate.
Edward must kill the slaver Laurens Prins as a favor to James Kidd before rescuing the man called the Sage from his imprisonment.
You must sabotage three alarm bells. The first bell is located directly in front of you. Jump down from the windmill and follow Kidd into the bushes near the first bell.
Kidd will coughing lure two guards toward him. Keep slightly to the side so they do not detect you - and then Kidd will quietly kill them both. There will be two soldiers remaining by the bell. Be careful not to be spotted by the watchman standing on the lookout tower - lure them into the bushes one by one, kill them, and then sabotage the bell.
Before heading toward the second bell, hide in the bushes under the tower and wait for the soldier patrolling the nearby road - lure him with a whistle and kill him. The guard on the tower should no longer have you in his line of sight, but if you want to, you can climb the tower and get rid of him.
The second bell is located a short distance to the southwest from the first one. While sneaking there, be careful not to be spotted by the guard patrolling the road - it is best to eliminate him quietly.
The second bell is guarded by a fairly large number of guards, but you can get rid of all of them very easily. Start with the one furthest to the left. Either sneak up on him or lure him toward you with a whistle.
Then, go around the buildings on the left side and hide in the bushes near the watchtower. Keeping in mind that there is a guard on the watchtower, lure the two guards walking near the bell toward you one by one and assassinate them.
Don't forget about the third soldier here standing a bit further away.
Next, climb the tower and deal with the marksman.
Sabotage the bell, sneak up behind the two soldiers hidden behind the crates - and perform a double assassination to get rid of them.
You can now head north toward the next set of buildings - as that is where the last bell is located. Move over there and hide in the tall grass. The area is guarded by a significant number of soldiers - but to reach the bell and sabotage it, you only need to take care of a few of them. Start with the soldier patrolling the area on the left side.
Move to the left and position yourself far enough so as not to draw the attention of the two soldiers standing under the shelter, and whistle when the soldier patrolling the area approaches to get his attention. Kill him when he steps into the tall grass. There is a chance that the kill will alert those two nearby soldiers and they will head toward you - in that case, assassinate them as well.
Return near the soldier with the axe standing close to the hay wagon, lure him into the tall grass as well - and assassinate him.
At the right moment, move to the bushes near the bell. Wait for another patrolling soldier to start walking away, quickly approach the bell and sabotage it - then retreat back into the bushes.
Simply approach the bushes near the entrance to the estate. Kidd will play his part, and after a short moment, the gate to the estate will be open - and its guards dead.
Go through the open gate and climb onto the roof of the building. Watch out for the guard on the balcony to the left and the open windows - as there are soldiers inside.
Kill both marksmen patrolling the roof. You can pull the one on the left side into the leaf cart.
You will need to sneak up on the one on the right from behind.
Next, jump onto the trees at the end of the right wing of the roof.
Move along the trees above the gazebo where Prins is located. An Air Assassination will do the job - and trigger a cutscene. Unfortunately, Roberts will turn out to be someone other than you thought.
Don't fight the soldiers - just run and avoid them. Sprint through the open gate on the right side of the estate.
Keep running straight and cross over to the other side of the fence using the leaning tree.
Stick to the right side and run along the stream until you reach the waterfall. Perform a leap of faith into the water - and you will exit the hostile area.
Return to the windmill, where Kidd will be waiting for you at the base. You will talk for a moment - and this quest will end, unlocking the next one - Diving for Medicines.
