From the introduction:
The characters have found 3 shells that contained whale-skinned books inside with strange colored runes on their pages. If the characters use a Comprehend Languages spell, they will be able to read the books. They are instructions to the lesser cleric in the Water temple on how to maintain the power of the Elder until the trap could be sprung on the characters. It seems that the head Sahuagin Cleric has gone off with Theleb to help in his new attempt to free the Elder from his eternal bonds. This Water temple was to be sacrificed so that the new plan could be undertaken. The only clues to where Theleb’s keep is in two small passages in the third book. It first reads as follows: "Theleb is a creators offspring and a powerful lord. He is surrounded with creatures like himself, creatures of death and destruction. His reign is in a place where the ancients worshiped our lord. A place so vile, damp and bog filled that creatures such as myself can exist there."
User summary:
For 10th - 14th level characters.