This is the fourth and final quest in the series where you hunt the Templar named Jing Lang to acquire her key. You can start it after completing the "Upton's Sorrow" quest. You can start it by talking to Upton, who is waiting for you near the swamp on Nassau island.
Edward must assassinate Jing Lang and recover her Templar key.
Vance is in a small camp on the hill on the other side of the swamp. The swamp is guarded by several pirates, and you must not forget about the crocodiles swimming in the water. You can reach him by following the tree branches, but the easiest way is probably to go around the swamp from the right side.
Once you reach the camp where Vance is, climb up the wooden poles...
and hide in the tall grass.
When Vance enters the tent, sneak up on him and assassinate him. You do not need to worry about the other pirates - they will despawn after you kill Vance.
Once Vance has been dealt with, Jing Lang will appear in the camp. Not wanting to share Vance's fate, she will start running after a moment. Give chase to her.
At a certain point, she will stop, and once two regular guards join her, she will attack you alongside them. Killing Jing Lang alone is enough to trigger a cutscene, after which the Templar Key will end up in your inventory.
Return to the camp where you killed Vance and talk to Upton, who is grieving the loss of his brother. He will thank you for your help, after which this quest will end.
