What is the theme in Raise the Titanic! by Clive Cussler?

The novel has a theme of intrigue and suspense from cover to cover. It begins in the opening pages when the Titanic is sinking and an unnamed passenger locks himself in the vault instead of trying to save himself. He tells a crew member that he has killed eight men and can't live with the guilt. As he closed the vault door, he mentions Southby. This sets the stage for the intrigue and suspense that follows.