On your way back to Tenebrae from the Cemetery, you are stopped by a guard who tells you that Bentic has been executed and that Devon has been arrested. He also tells you that you are under suspicion since you were seen with both of them.
Before proceeding with your studies in Necromancy, it is necessary to find out what is going on. Devon is now located in the dungeons beneath the palace in Central Tenebrae. Go into the palace and find the stairs down in the west wing of the palace. I took the trouble of mapping the dungeon so that you can see the area more clearly. In the dungeon, go east and find the metal wall. On one side of the metal wall is a plaque, while on the other side is a lever which lowers the metal wall. Naturally, pull the lever to lower the wall and go through. Kill the skellot and go and talk to Devon.
Devon tells you to ask Salkind what is happening. Salkind lives in East Tenebrae, and you can't miss his house because it is surrounded by a wall. When you interrogate Salkind, he tells you to consult his log book. His log book is on his desk, and it says that Bentic has been executed for conducting forbidden research, which is in the dungeon evidence chamber. This is a hint to what you need to do next.
Recall to the Plateau and talk to Mythran. Buy the scroll of dispelling magical portals from him (it costs 50 obsidian), since it is very important. Once you have the scroll, recall back to Central Tenebrae.
Go back down to the dungeon, and go to the eastern end, until you see a pink book in a room with no entrance. Use the scroll to dispell the magic sealing the room, and go in and read Bentic's Journal. You will learn that Devon is the rightful Tempest while Mordea is only the second born. However, after you finish reading the book, you will be caught by three guards.
Whether you choose to go with them quietly or by force, you end up on the docks, ready to witness the execution of your friend Devon and follow his fate.
Watch the execution, and when you get a choice, say that Devon is the rightful heir and that you have proof, but do not insult Mordea or you will get killed. You can read what happens in the execution in my dialogue section. Basically, Devon becomes conscient of his powers and uses them to dispose of Mordea. Devon will then walk away on the water to contemplete the current events.
Following Mordea's lightning attacks during the execution, the three guards escorting you are dead, and both Shaana and Darion are unconscious and in pain, and cannot get up. If you want to have some fun, attack them. You will notice that they were only faking, because they get up very quickly to fight back.
Now that peace reigns in Tenebrae, you can get on with your Necromantic studies. If you are interested in Thaumaturgy, Mythran will now sell you Confusion Blast.