From the introduction:
Long ago, the Mage-King of Iltkazar, the Lord-most-mighty Shoon, created a grimoire of his greatest magics. An evil and twisted man, Shoon slew a dozen unicorns and used their blood to magically bind his soul to this workbook. Upon the magical text he spun numerous other enchantments, including one which hides its words from sight and another which imprisons careless readers. Shoon finally died and his soul came to rest in the grimoire; a large unremarkable spell book with blank pages that had earned the name, the "Tome of the Unicorn". Shoon continued to exist within the book's back cover as a demilich, a rare but powerful undead spirit which is unturnable and practically invincible. The book passed between the hands of many a wizard in the days after Shoon's death, many of these dying as soon as Shoon's new form drained their souls unexpectedly.
For 7th - 10th level characters, including at least one paladin and one mage.