This module contains background information, a large-scale referee's map with a matching partial map for players, referee's notes, special exploration and encounter pieces, a large map detailing a temple complex area, encounter and map matrix keys, and an additional section pertaining to a pair of unique new creatures for use with this module and the game as a whole. A complete setting for play of ADVANCED DUNGEONS & DRAGONS is contained herein. This module can be played alone, as the second part of a series of three modules (with DESCENT INTO THE DEPTHS OF THE EARTH, D1, and VAULT OF THE DROW, D3).
The next installment in the Drow series features an underground temple of the kuo-toan species, who are modeled after Lovecraft's Deep Ones introduced in The Shadow Over Innsmouth. The adventure will either play out in one of two ways: (1) the party makes the proper homage to the kuo-toan temple and just moves on or (2) they fail to do so, and an out-and-out battle results against all the guards. The fish-men are tough because of their unusual weaponry; sticky shields and harpooning spears. The party has no reason to fight these foes if playing through the D series, so I suspect in that context most of this adventure wouldn't get used. Played on its own, perhaps as the terminal area of an Innsmouth adventure, it might go to better use.
The second module in the D series, in which players explore the underdark, this module introduces us to a couple of iconic D&D races, one of them is right there in the title, the Kuo-Toa, Lovecraftian fish-people and their goddess Blibdoolpoolp (hence Sea Mother, because I can't be bothered writing that again). In fact the climax of this module is the titular Kuo-Toan shrine to the Sea Mother.
Before that, however, you get to meet the Svirfneblin (hence Deep Gnomes, because again I can't be bothered typing that out, or pronouncing it in my head), a overall neutral to good race which can become valuable allies to the party as they go down deeper into the underdark. It's also convenient that they hate Drow, Kuo-Toa and Illithids, all the enemies that the party has to face down here.
It would, however, be a mistake to go through this module swords blazing, there is a lot of interesting politics, religion and social structure to the Kuo-Toa that would be lost in a hack and slash approach. There are chances for some great role playing here, particularly if the characters impersonate pilgrims to the shrine of the Sea Mother where they might even be teleported to the Elemental Plane of Water and get to meet her with some dangerous but cool consequences. This is a pretty nifty module which can be good or great depending on the approach taken by the party