sentences:  After several expeditions it becomes clear that the worms, together with bacteria, are destabilizing the methane clathrate in the continental shelf.When the continental slope collapses the subterranean landslide causes a tsunami that hits most of the North Sea's coasts, killing millions and severely damaging the infrastructure in the coastal regions.At the same time Leon Anawak, a marine scientist who investigates the behavior of whales and works for a whale watching company, makes startling observations in the whales' behavior; and is called to investigate an incident where whales and sea-borne mussels seemed to have attacked and incapacitated a commercial freighter.