In this chapter PCs can find two components that Vizeran needs for the ritual: a Purple Worm's egg and the main eye of Beholder.
Party must go to the Wormwrithings, a labyrinth of tunnels scavenged in the rock by Purple Worms' movements. The place is a nest for many of them think.
Vizeran also is sure: a Beholder lives there.
You can also find a Beholder's eye by completing a side-quest of Chapter 9.
You'll find a specific random encounter table for this area.
There's no map, due complexity of the area. It's up to you to stimate the time needed for moving throughout the tunnels. Try to have at least a couple of random encounters and a short rest.
You'll find also an encounter with a tribe of Troglodytes which is tearing apart by a little civil war.
The Purple Worms' nest, whose map is in the book, is the typical cave-dungeon but complicated by Worms moving and suddenly opening new passsages and by a Drow group who's looking for eggs.
Drow are looking for eggs only for money. They want to sell them to mages since is a highly valuable spell component. You can let your players believe that others are trying to make the ritual.
The Beholder encounter is much more linear. The party enter in its lair and attack the monster. The battle can be interesting since it's likely to happen on a bridge.
PC will find a huge treasure and many slaves that can be taken as allied NPCs and can give some useful informations for the following adventures.