The Ostrich
Initiate this by talking to a woman who is talking to a door, north across the river from Mefkat.
As with so many problems Bayek encounters, the solution is to kill a tax collector. Track him down in nearby Camp Shemu.
Like other tax collectors, he has two guards, plus whoever is manning the camp. If you've already cleared out Camp Shemu, then you've got a straight shot at him, otherwise approach the camp from the water and clear the soldiers east to west. Either way, killing the taxman instantly ends the mission.