The Hyena (Main Quest)
Note: The Enhanced Predator Bow ability will be extremely useful in the final fight of this quest.
The Hyena is the Order operative in Giza, so to Giza you must go to begin the quest.
Your marker will lead you to a shifty merchant in the market.
First he'll hold you up for 100 drachmas. Pay him, and he'll then extort you to go 'recover' his horse. In return, he gives you just enough Hyena info to keep you on the hook.
Go to recover his horse from the Depleted Quarry Hideout. He'll send two NPCs with you, but after their dialogue ends, ignore them as much as possible.
Even if you cleared it before, the Quarry will be nearly fully staffed again, lacking only command officers. The horse will be in the middle, on the lowest level, just at the mouth of the clearing.
Approach from the sides of the canyon. This a good place to ditch your NPC helpers- try to get them involved in fights, then sneak away. They tend to ruin your assassin mojo.
While they're doing that, you can snipe or stealth kill the two horse guards, and secure your prize.
Since you're in the area, you may also wish to release the prisoners in the main camp here. Even if you released them before, more will have materialised.
When ready, mount the horse and ride out of the canyon. It's strong enough to take a few arrows, so you can just blow by the guards here if you like, or engage in a little horse combat if you'd rather.
When ready, ride all the way back to Giza. Mered will be in a slightly different place, so just follow your marker.
Mered will finally give you the goods on the Hyena, and set an objective point out to the west.
Ride on out. This is rough country, so you can expect a few random encounters with wild animals and bandits as you go.
Follow the main road up into the hills.
This will lead you (with Senu's help) to a hyena lair. Of course.
You don't need to clear out the hyenas, but it is an awful lot of soft leather in one place. The alpha, though, will probably be in the camp above.
That camp is an investigation area. There are several clues to find, here (you'll want to free the caged man just so he stops screaming) but the one that advances the plot is inside the hyena cage.
Open the cage, and slay the hyena, then investigate the loose brick at the back.
This reveals a secret map, and give you a new destination- the Pyramid of Khufu.
Travel to the pyramid. If you've already climbed it, you can fast-travel right there. Either way, follow the marker. It'll be easy to tell where the entrance is, because it'll be surrounded by hyenas.
Destroy them for more soft leather and tomb access, very near the base of the pyramid
You'll want to use your torch here. In general, when tracking the Hyena at least, you'll want to go down wherever possible. Your first chance is a crack in the right hand side of the tunnel, which the game politely reminds you can be entered.
Squeeze through. The Hyena will sneer at you some more, which is another continuing sign that you're on the right track. The passage here leads to a larger room with a large hole in the floor. Drop down.
Follow the passage past the already-lit brazier and the now-harmless trapdoor to a strange tomb.
This is an investigation area- one of the ones where you'll need to examine every clue to proceed. Those clues are- the freshly opened corpse,
The written, chalky symbols (as opposed to the glowly golden ones),
and the small waxy pile of offerings.
This gives Bayek all he needs to re-imagine the ritual.
Return to the sarcophagus and open it.
This triggers your first face-to-face with the Hyena, but ends with her fleeing. Before you follow, carefully scour the chamber here for silica- there's lots of little bits about.
When ready, follow Hyena's trail through the scarab'd door.
As you make your way along the passage, Hyena will occasionally pop up to shoot arrows at you and trigger traps, but these attacks are easily evaded by simply falling back a little ways down the tunnel, until she's stopped firing, and/or the flames have gone out.
Climb up the shaft at the tunnel's end, and refill your arrows if you need to.
Emerge into a sandstorm, with low visibility, and no Senu.
Wander outside-but-not-far-from cover to lure Khaliset into firing on you. Her burning arrows reveal her position, so fire back with the Predator Bow or Hunter's Bow. The Enhanced Predator Bow ability is extremely useful for ensuring headshots here.
Every time she's hit, she'll disappear to another location, so rinse and repeat. When she's at about two-thirds health, one of her hyenas will attack. Engage with spear or warrior bow- Haliset's hyenas can pounce and knock you down if they get close.
The second appears when she's at about one-third health, and the woman herself won't be far behind.
Tear into her with a fast blade- she's not very tough, and has no blocking ability. Using adrenaline should end this in a matter of seconds.
Confirm the kill for a more-depressing-than-usual afterlife sequence, and mission completion.
It is a little unusual that a mere scavenger/serial-killer was a full-fledged member of the Order, rather than some sort of hireling or lackey, but then the Order's hiring practices are extremely mysterious.