This quest is unlocked after you learn where to find the people Antó is looking for - which means after completing "The Maroon Assassin" quest. You can start it by speaking with Antó again.
Edward helps Antó free slaves in exchange for information about the Templar and his key.
Follow Antó and he will lead you near the location where the first of his friends is being held.
Three locations will be marked on your map, indicating where you need to go. The first one is right in front of you.
Antó will suggest using the local drunks, and indeed, you can find them right nearby. However, you can also handle this entirely stealthily. To do that, start by climbing the trunk of the leaning tree, then move across the branches above the restricted area.
Do not try to hang or perform an air assassination on the guard standing below - this would alert the other guards - just jump into the leaf pile instead.
Drag the guard into the leaf pile and kill him. Shortly after, Antó should quietly double assassinate the guards standing near the entrance.
Sneak up to the two guards standing near the prisoner, double assassinate them, and then free the captive.
When you reach the second location marked on the map, you will see four soldiers escorting the next Maroon through the streets of the city.
You can sneak up on them from behind or perform an air assassination to quickly take out two of them, and then defeat the remaining two in open combat.
If you are patient or simply curious about where the soldiers are leading the prisoner, follow them. After a while, they will reach the other side of the town, where the prisoner will stand inside a small shed while the guards position themselves around it. At that point, you only need to lure one of them into the tall grass and assassinate him...
...allowing you to sneak up to the prisoner and set him free.
Approach the last marker from the southwest side. There, you will find a hole in the fence that lets you slip into the restricted area.
Hide in the tall grass, and when a patrolling soldier gets close, drag him in and kill him.
Next, get rid of the officer standing by the prisoner and set the prisoner free. The guards standing at the gates shouldn't notice a thing.
After freeing the prisoner, leave the restricted area the same way you came in.
The officer and three soldiers accompanying him are pacing back and forth along the city's main street.
Position yourself above them and - at the right moment - execute an air assassination, preferably on the officer himself, then finish off his companions.
Return to Antó - he will be waiting for you near the location where you rescued the first Maroon. Speak with him briefy, and this will finish the quest and unlock the next one - Under Attack.
