From the Introduction:
Shadows Under Scant is a module set in the World of Greyhawk and designed for 2nd edition AD&D rules. The action takes place in (and under) the City of Scant which is the capital of Onnwal, founding member of the Iron League. It should be noticed that this adventure takes place in 576 CY, 7 years before the Greyhawk Wars during which the Scarlet Brotherhood and their Hepmonaland minions captured Onnwal.
Players will only need the 2nd ed. Player's Handbook to participate but it is recommended that the Dungeon Master (at the minimum) have access to the 2nd ed. Dungeon Master's Guide and Monstrous Compendium. In addition the Monstrous Arcana supplement "The Sea Devils" should prove beneficial.
It would also be prudent for DMs to take a few moments to review the rules for fighting in and underwater as laid out in the Dungeon Master's Guide, p109-112.
The allotted time span for this module is half an hour for set up followed by a further 3 hours of actual game time. After 3 hours play should be halted and the character sheets gathered in for scoring. Italicised text may be read to the players.