Attention: Wikipedia contains spoilers
The story is about an underwater oil drilling rig that is send by the US military to examine a lost submarine, which leads to an international crisis bordering on a new world war. It turns out that at the bottom of the name-giving abyss near the crash site of the submarine, an underwater city of water-dwelling aliens is located. A Navy Seal, suffering from pressure sickness, turns paranoid and tries to destroy the city with a nuclear weapon from the crashed submarine. The aliens, in turn, threaten to destroy all coastal regions of the world by giant tsunamis.