Go to the Great Library (east from Raven Dust crypt entrance) and speak with Filandrius. Say “Foreign magic”, “Need”, “Filnar'thir”, “Darkness”, “Get it” and he will send you to kill Anthor the Mad and get the Tome of Arcane Knowledge. Go to Stoneheim and find Anthor the Mad (located northeast from spider cave entrance). Kill him and you will receive the Tome of Arcane Knowledge. Return to Filandrius, click on him and he will take the Tome of Knowledge. He will reward you with a Belt of Unstable Protection and a Gem of Unstable protection. You can also learn from him new spells.

Rewards: Belt and Unstable Protection Gem (0 stats) - Possibility to learn new spells NPCs involved: Filandrius Mini-boss involved: Anthor the Mad