Follower or Leader (Side Quest)
A side quest in Heb Sed. The only side quest in Heb Sed, actually.
Speak to Setna in the Valley of Scorpions to get this one started.
He needs some scorpion's blood, and since Bayek should be killing every scorpion he sees, this works out well. Kill and loot the plot-markered scorpion in the vale to get the usual crafting components, and a small jar of blood.
Return to Setna for a brief cutscene, and new objective in the Caves of the Valiant.
Ride for the the Caves (nothing says 'honored dead' like a good cave). Scans will show your goal by a hidden passage toward the east of the complex.
Use the bushes and/or ledges by the entrance to kill or sneak your way in.
Make a beeline for the plot marker. Again, use the shrubbery to sneak or sneak-kill past the guard.
Slip into the catacombs.
Use your animus scan to find the Ankh- it'll have a gold marker.
Grab the Ankh (no ambush or trap is triggered), and meet up with Setna northwest of the Caverns.
Your new goal is to recover the Postiche (which is one of those stylized ancient Egyptian fake beards). It's carried by a patrolling jackalman in the Pavilion of Judgement area. Kill him and his guards to secure the item.
With all the trials completed, follow your marker to a rock outcropping, and enter the caverns from the northeast.
Meet up with Setna one last time to see him confront his famous father, who's uncharacteristically cool with the whole thing.
This completes the mission, and grants the legendary Mut's Sorrow shield.
You can also poke around the scrolls here for some fun tidbits.