Raetommon has gone deep into the Oldwalls with Forge-Bound Master Zdenya. The Voices of Nerat wants the Forge-Bound Master found and sent to him along with Raetommon if possible.
Make your way towards the north-western corner of the location, picking up the Rho Torchkey on the way. Use it to power up the beacon. In the beacon room, use the Citren on the upper left beacon, Rho on the central, and Amith on the upper right beacon to activate the floorplate.
Approach the central platform to confront Raetommon. After wading through his gloating, indicating that he's gone completely bonkers, you can attack or intimidate him (Athletics 52) to hand over the torchkey. The latter option causes him to attack, but he does so without the support of the Bane or the Havoc.
Use the torchkeys on the beacons to return outside. The Emir (green) goes to the lower left beacon, Citren (yellow) to lower right, Rho (red) to upper left, Amith (violet) to the upper right.
Crap. After three torchkeys are activated, the Havoc wakes up and attack. Kill it. Pick up the Greater Healing Potion recipe from its remains.
Head upstairs. You can free or kill Zdenya. In the former, send her to Nerat. In the latter... Well, the Archon won't be pleased. You also have the option of sending Raetommon to Nerat.
Go to Eldian and talk to him. Decide what to do with the Magebane. Note that a Chorus garrison is now stationed at the Crossing (if they were not already there).