What is the theme in Deep Six by Clive Cussler?

International conspiracies is the main theme of the book. The novel begins with the discovery of a nerve agent accidentally released into the ocean, to the kidnapping of the President of the United States and the three men who would succeed him to the Presidency, and ends with the impeachment of the President. All these incidences seem unrelated, but Dirk Pitt quickly begins to see a connection among them all. The nerve agent is aboard a ship that was once stolen on the high seas and whose name was changed illegally