Bad Faith (Side Quest)
This quest becomes available after completing Jaws of Sobek. Meet up with the priest you freed then to find him having laid out a couple of attackers.
The two of you will agree that Sehetep needs to die, and that Bayek needs to kill him. The moment you leave the compound here, a squad of Sehetep's men will ambush you, including those obnoxious smoke screen ninjas (that sort of thing is only cool when *you* do it).
If this encounter starts to go against you, try dropping over the side of the bridge, where you can then execute the hostiles one by one as they follow you.
When clear, return to the Temple of Sobek, and pinpoint your target performing rituals in the main temple.
Climb up the outer wall to avoid the guards, and then hop across from the inner wall to reach the temple roof.
Slip in through the upper windows to enter unobserved.
Sehetep only has one guard with him. You can either clamber down the central statue angling for a chainkill (in which case you'll want to take out the soldier first, as shields can block chainkills), or just snipe the pair of them.
Confirm the kill, though there's no Duat sequence for the ex-priest. Too bad- he seemed like real Order material.
Exit the way you came, and meet Padiaset just outside the front gates. Speak with him to complete the mission.