There is a brown tide infesting the ocean off the shore of Nicaragua. The twins are working in a NUMA(r) 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 not only for them but also for a luxurious floating resort hotel square in its path. The peril for everybody concerned is incalculable, and, desperately, Pitt, Al Giordino, and the rest of the NUMA(r) crew rush to the rescue.