Part 1: Rescue
This mission is essentially a whole bunch of pirate rescue mini-missions that you find in the major settlements. You need to approach each load of casualties without being spotted (sleep darts are great for this), deal with the guards and then interact with the prisoners to free them.
We need to free twelve prisoners in total to complete the mission and there quite a few more than that available. Note that getting spotted will have the guards attack prisoners, so if this happens get in there quick to stop it as you only have a limited number of casualties to play with (see the bar on the left of the screen).
It is really self-explanatory, use heights or stalking zones to approach each situation, use sleep darts to deal with any gunners and any other guards that you feel you need to, kill the captors and free the captives. Rinse and repeat. You can even go into conflict mode next to hostages, as long as you deal with the guards pointing their guns at them quickly.
Once you have freed twelve of the prisoners, a scene will play. Afterwards, follow your new friend to the locked door by the waterfall nearby for an explanation of a side-task we can undertake later, whilst off-mission – the Native Pillars.
Part 2: Rescue
Once you have finished with the natives, return to the Morrigan and sail across the water directly to the west. Dock and head inland and as you go you should notice some burning bits and pieces littering the area.
Keep moving and you’ll come across a group of British soldiers under attack. At this point a health bar will appear on the left side of the screen and will diminish quite rapidly. We essentially need to clear out all of the enemies from the area as quickly as possible. The game wants us specifically to take down the captain, who is conveniently located on the path that we take up from the beach and once the rest of the baddies have been dealt with, cut down the flag.
This will result in a scene to end the mission.