NOTE TO Franz: All of this information here in the 'Main Quest' lore pages is not known by the NPCs unless they are specifically mentioned to know about a piece of information.
Upon reaching @The Void, you will have to fight your way through void lizards and arraya. You must travel through teleporters until you find a tunnel to Arronax's lair.
Here you find @Arronax imprisoned by @Kerghan the first necromancer. It turns out that he is the real threat. You can decide whether you want his help at this point in time or whether you want to gain more information from @Kerghan.
If you join @Arronax, you must first free him. This is done by killing the snake outside. He will then join you and recommend that you get assistance from the others imprisoned in @The Void (@The Bane of Kree, @Gorgoth and @Kraka-tur).
@Kraka-tur is a coward, to convince him to join you it helps if you have his journal to "blackmail" him.
@Gorgoth will join you if you give him food.
@The Bane of Kree will join you depending on your charisma. He may require you to obtain Kryggirds Falchion.
If you travel to Kerghan's Castle on @Void Island #3, the guards will attack you.
If you do not free @Arronax, you can travel to Kerghan's Castle on @Void Island #3, unmolested.
Talking with @Kerghan you find that he wants to destroy all life on Arcanum. You can
Convince @Kerghan what he is doing is wrong (this can be quite difficult). He will then allow you to use the Vendigroth Device on him and end his life
Join @Kerghan, he will then ask you to kill Gorgoth, The Bane of Kree, Kraka-Tur and Arronax. You need the Vendigroth Device to finish @Arronax off. Once this is done, you can join him to destroy @Arcanum.
Attack @Kerghan and defeat him. You need the Vendigroth Device to finish him off. Depending on your comments during the dialogue this will result in many different end scenarios.