Kingdoms of Amalur: Reckoning - Enemies in High Places

Once you've killed the assassins, talk to Hugues. He will send you to Adessa to talk to Templar Jorielle. This will go less than well but that's the plan. Go downstairs and on your way out, you'll be stopped by her aide. Go outside and follow the Quest Marker to where Octienne is. He'll fly off in a fit of rage after a short conversation and you'll be attacked by his two guards. Kill them and then go up the hall and out the door to the balcony.

Octienne

This is a tough fight. The first part will take place on this funky walkway. Watch for the archer on the nearby building. One hit should take him out so do it. Hit Octienne a few times and he'll move far away. In the meantime he'll be casting frost spells at you. It's possible to interrupt him but not often. Keep hitting him and dodging the ice balls. When he finally moves, follow him to the end of the walkway.

He'll be behind a magical barrier and you can't harm him. You'll have to fight a group of three assassins while he shoots fireballs at you. Thankfully these fireballs don't do much damage but they do stun you. My recommendation is to go to the SE corner of the platform because there is some scaffolding in the way that will protect you from his attacks allowing you to only fight the three assassins.

Once they are dead, Octienne will retreat. We're going to use a little trick at this point to beat him. Stay on this platform. Eventually Octienne will come back towards you and ready a spell. Hit him with some kind of ability to knock him off balance (Just marking him with Mark of Flame was enough). This will cause him to retreat. Keep doing this until he stops coming. He will set up another shield. Go along this catwalk and there will be an archer on either side. Get rid of them and proceed to the large platform at the end.

When you get there, you won't be able to retreat and you'll be attacked by four assassins this time. You also have no place to hide so I would recommend a Fate Shift at this point. Clear out the assassins and then pull the same trick on Octienne. Wait for him to come and cause him to teleport. Once he stops coming, go down this final path and watch for the two archers on the left. At the last platform, there will be more scaffolding on the right that you can use to protect yourself. Get behind it and then kill the assassins which will allow you to attack Octienne again. This part will go much like the first section. Knock him down and then finish him. Once he's down for good, jump down into the Forum.

You'll talk to the Templar Jorielle again and then Hugues who will send you to Klurikon in search of Ventrinio. For now, it's better to take the Great General if you already haven't.