Where the Slaves Die
This mission is added to your log after speaking with Tahira in the Hidden One's Bureau.
Follow your marker to a ledge overlooking Operum Tuorum Gemmam Castra, and speak with Tahira again.
She'll clue you in on the local villain Tacito. Night or day, he'll be giving a speech to the camp when you make your move, so there's no completely stealthy way to kill him, though there are stealthy approaches.
However, you're going to have to exterminate everyone in camp in a few ticks anyway, so unless you're itching for some melee, there are easier ways to proceed. Climb and claim the guard tower in the northeast corner of the camp.
There are two arrow caches up here- if you've fully upgraded your quiver, then that's 30 predator arrows- more than there are hostiles in bowshot. Plus, (while this may have been a temporary glitch), the right hand arrow rack seems to self-replenish if you snap into Senu-vision and back. Use this bounty of ammo to rain down some death-from above, starting with Tacito.
This is also a good time to snipe the camp captain.
When you've pinned the lot of them, hop or slide down and confirm the kill, leading to a brief-but-disturbing cutscene, and the end of Tacito.
You may want to free the prisoners here as well. As always, they'll start rampaging once they're loose, so think about gathering up treasure and trapping braziers before springing them. Still, it's a good idea to let them (and other camp captives) loose before advancing to the next step.
When ready, follow your marker to Tahira, who reports on incoming hostile force. Join the rebels in cutting them down, along with any other surviving hostiles.
As always, a yellow marker will indicate the last few surviving soldiers, as their numbers dwindle. When the last has been dispatched, follow your marker and speak with the rebel leader.
This conversation completes the mission, and activates a rebel presence in the Sinai.