From the publisher's website:
A Pathfinder Roleplaying Game compatible aquatic adventure for 7th-level PCs by Marc Radle.
Only a few miles from a small seaside town, the mysterious underwater edifice known as the Sunken Pyramid lies hidden beneath the waves. The handful of sages and scholars with any knowledge of this massive stone structure debate whether it is a completely natural rock formation, a natural site that has been intentionally modified or something built long ago by human, or inhuman, hands.
Locals and ship's crews alike report signs of increased sahuagin activity in the waters around the Sunken Pyramid. Is the recent rash of disappearances and abductions which have plagued the area connected in any way? Can these abductions be stopped before even more people are taken? Can those already abducted be found and rescued? And what of the strange and often conflicting rumours which whisper of something far more terrible lurking far beneath the Sunken Pyramid?
In addition to the adventure itself, the module contains extensive background on sahuagin culture and tribal society as well as complete statistics and motivations for all key members of the sahuagin tribe.