Mysterious chronicle (part 18) is a book found only in Daemonheim. It may appear in front of the dungeon-ending ladder after killing the boss monster.
It was written in the year 1724 of the Fourth Age. Bilrach had a rebellion uprising against him, but he stopped it before it had a chance. Astea Frostweb and Lexicus Runewright stood up to Bilrach with their combined magical abilities but failed. He separated them to discourage further uprisings.
Details leading up to the attack can be found in Astea frostweb's journal and Lexicus runewright's journal. They found out Bilrach's true plan and wanted to stop him, as it seems Bilrach must be leading his followers on, or at least the ones that have arrived recently from the surface. This was hinted at in the previous chronicle.
Year 1724 of the 4th Age:
A disgrace! I thought losing servants out of fear to the depth was bad, but now rebellion? I quashed this before it had a chance. Two treacherous fools dared attack me? History will mark this day: the day Astea Frostweb and Lexicus Runewright were enslaved by the mighty Bilrach and split for all eternity. They thought their combined magical ability could stand up to me? Small-minded fools! They will never be together again and will serve my purpose as guards of my great dungeon forever. There will be no further uprisings after that demonstration.Zamorak be praised!