On one of the sea towns that navigate the oceans of Nuclearth, people are being found floating between the ships, drowned. While it certainly happens that people in the sea towns do occasionally fall off the boats into the water and drown, it's happening now in numbers far greater than the usual. Finally someone spots a tentacle wrapping around a victim and yanking them overboard, confirming that the drowning deaths are no accidents—something in the water, most likely aquatic mutants, is intentionally pulling people into the water and drowning them. Why are they doing this—and how can they be stopped? In order to confront the murderous mutants, the PCs will have to enter the water themselves—and take them on in their home territory.
