The group splits up to try and take the Sahuagin by surprise on all fronts through the two entrances they find. The front entrance group is met with opposition as the water flowing from the cave is too strong for them to go through. They eventually get to the other entrance where the other group is fight a group of Sahuagin who attack without mercy.
The party begins to explore the various caves and fight off more Sahuagin, Darkmantles, and water elementals. The group also finds various treasures in one room and while resting in that room they are confronted by a group of Myconids. Led by Valika, the sovereign of their troops of fungus creatures, the myconids are able to make friends with the Inheritors telling the humanoids that Sahuagin have desecrated their lands and want them off their home turf. The heroes agree to help them and the Myconids say they will protect the eastern border from other Sahuagins coming.
The heroes continue west towards the rushing sound of water. They find themselves next to a large Underdark lake with an island in the middle of it.