Dirk Pitt battles his most dangerous foe ever with help from a very unexpected source. There is a black tide infesting the ocean off the shore of Nicaragua. Whilst trying to determine its origin, startling things begin to occur and the inhabitants of a floating resort find themselves directly in the path of a violent storm.

Dirk and the NUMA crew rush to their rescue, but they discover that there is an all-too-human evil at work and the black tide is only a by-product of its plan. Soon its work will be complete and the world will be a very different place.