Caverns of the Fish-Folk

From the introduction:

The Kuo-Toa Caverns [sic] is an adventure supplement for characters level 1-3. For use as a one off (2-4 hours), or as a campaign supplement. The players begin by meeting Tomen, a shipwrecked halfling, whose brother has been abducted by Kuo-Toa living off the coast. Tomen washed ashore on this forlorn coast thirteen years ago, and will do anything to escape, but first he must save Silvus, his younger brother, from the sacrificial fanaticism of the fish-folk. In addition, Kertol, Prince of the sprites has a bone to pick with the halfling brothers over the destruction of his summer court.