Curse of the Pharaohs II
After dispatching both Nefertiti and Akhenaton, speak again with Isidora in the Temple of Karnak. It's hard to see how Bayek can call his journeys a trick of mind when he's actually carrying the undead pharaoh's sword in his hand, but Isidora doesn't call him on it.
You will be interrupted by soldiers. You can ambush them or simply slip into the night (which seems like it will cause less trouble for Isidora). Either way, your new goal is to search Tychon's Villa.
The place is crawling with guards. As usual, a good strategy is to start at the roof and clear away the hostiles.
You don't need to wipe out the ground floor troops just yet. The documents you seek are on the upper level, accessed from outside, behind a slidable crate (if you've already investigated this location, you'll remember a location treasure being here).
Smash through a wooden screen to enter the room, then search the brown chest by the door to spark the Blood in the Water questline.