This is the final Templar Hunt quest for Opía Apito. It is unlocked after completing the "Right-Hand Man" quest, and to start it, you must sail to Castillo de Jagua to meet with Opía.
Edward must assassinate Lucia Márquez and recover her Templar key.
Follow Opía. After a short while, you will run into the first two guards. You can try to sneak past them quickly double assasinate them. but it is best to wait until they split up, then kill them one by one - first the one closer to the water, and then the other - before moving on.
As you approach the second pair of guards, Opía will ask you to kill one of them - the one standing on the right and marked with a target marker. Opía will take out the other guard.
When you reach the ruins, you will need to assassinate another guard, this time a sniper standing in the ruins on the left - Opía will take care of the one on the right.
Follow Opía and approach the ruins and the next guards from the right side. Opía should run into the ruins through the entrance on the right and take out the Brute standing inside. You should quickly approach the two guards standing outside and double assassinate them.
Note: It might happen that Opía fails to kill the Brute - in that case, enter the ruins on the right, sneak up on the Brute from behind, and finish him off.
The area on the other side of the ruins is occupied by seven of Márquez's men, and your task is to kill them all. You can do this in any way you like - for example, by using the small gunpowder barrels scattered around - but you can also try to do it stealthily. The biggest threat seems to be the marksman standing on the elevated platform on the opposite side.
If you prefer a stealthy approach, you can try repeating my method. I started from the left side. I hid in the tall grass and whistled to lure one of the guards over.
Next, I lured the second guard patrolling this side in the same way.
Then, I snuck around the right side to get behind the marksman and took him out quietly.
I jumped onto the stone pillars and double assassinated the two guards standing together in the middle.
Finally, I snuck up on the guards on the right side and took them out one by one.
As soon as you kill all the guards, you will hear Opia being attacked and calling for help. The location where she is will be marked with a target marker.
Opia will likely be fighting two soldiers, but these are not the only enemies. Another marksman will appear on the platform,...
...and one more soldier as well as a Brute will run in from different directions. You must kill all of them.
Once all enemies are dead, revive Opia.
Hint:
Lucia is hiding nearby. Trigger Eagle Vision and you will locate her with no problem.
Once you get close to her, she will start running east and stop at a cliff, where two soldiers will join her. Taking them all out should be a mere formality.
When you do this, approach Lucia's body and confirm the kill. This will earn you one of the four Templar Keys.
To complete this quest, speak with Opía once more - she is waiting right nearby.
