Way of the Gabiniani (Main Quest)
Continue the main quest by visiting Cleopatra in Herakleion Nome.
Follow your waypoint to start a conversation with Apollodorus and then Cleopatra. It's a little tense.
Follow Cleopatra. Be sure to loot the small jewelbox she walks past- it has a carbon crystal in it.
When your walk ends, you'll receive Cleopatra's gift- an Order informant. His info will point you toward nefarious doings in town.
Note that there is an informant table here as well.
Collect any quests you like, then head for the brothel. One doesn't like to point fingers, but this is like the third brothel Bayek's had to visit so far. Apparently, this is a Medjay tradition.
Pay the madam, though it's not clear that money actually changes hands. Go upstairs and wait for the twins. Badly beaten by Venator and his cronies, they're only too happy to give him up.
Follow your marker, and slip into Venator's place through the balcony.
There are blue-triangle points of interest upstairs, but the investigation area is only downstairs- one of the ones where you need to check everything to proceed. Those things are the dummy head full of arrows,
the snake jar, which you'll need to smash and search for a letter (and a snake),
some make up and accessories on a couch,
and some wine bottles.
From this, Bayek deduces Venator's plan.
You can stop the whole thing dead with three arrows. First, head north to the lighthouse. The assassin archer here is clearly your top priority. He paces back and forth a lot, but a good predator arrow will be able to account for him.
Now turn east, running along the roof tops to the dock. There are a lot of soldiers and a lot of oil, but you only need to kill the one guy to meet your objective here.
So that's arrow two.
The last arrow goes into the skull of the female impersonator near the central pool. Be ready to duck back into the shadows once the arrow hits, but those three clean kills complete this part of the mission.
Return to the palace for a cutscene, then an attack. The enemy soldiers just walk in up the front steps.
Cleopatra's guard are actually pretty good fighters, and with their help this is an easy battle. However, those guards disappear for the second stage the battle, against Venator.
Venator hits hard, but he's not that difficult an opponent. Wait for him to do one his flamboyant leaps or charges, then attack while he recovers his stance.
He has no shield, so light and warrior bows work well if you need a breather from hand-to-hand, and use your adrenaline strike whenever possible. Maintain these tactics for the final kill.
A cutscene will send you and Aya to the far north of the map to meet Ptolemy. Grab a boat and head out.
The camp is full of dead men, but there is no ambush here- go to your marker to launch a final cutscene.
This completes the mission.
Note that this is last Main Quest mission you can perform in the open world for a bit. After this, you'll be tied to the main quest for a while, though you will be able to go back and address all unfinished business later.