At the end of Valhalla Rising, Dirk Pitt discovered, to his shock, that he had two grown children he had never known about, twenty-three-year-old fraternal twins born to a woman who he thought had died in an underwater earthquake. Both have inherited his love of the sea: the girl, Summer, a marine biologist; the boy, himself named Dirk, a marine engineer. And now they are about to help their father in the adventure of a lifetime.
A brown tide is infesting the ocean off the shore of Nicaragua. The twins are working in a NUMA® underwater enclosure, trying to determine its origin, when two startling things happen: Summer discovers an artifact, something strange and beautiful and ancient; and the worst storm in years boils up out of the sky, heading straight for them—and for a luxurious floating resort hotel square in its path.
The peril for everybody concerned is incalculable, and Pitt, Al Giordino, and the rest of the NUMA® crew desperately rush to the rescue, but what they find in the storm's wake makes the furies of nature pale in comparison. For there is an all-too-human evil at work in that part of the world, and the tide is only a byproduct of its plan. Soon, the work will be complete—and the world will be a very different place.