What is the theme in Plum Island by Nelson DeMille?

There are many levels of greed in this novel. Tobin's overwhelming desire for money and power is the most obvious, but John is just as guilty of desiring and pursuing a goal based on greed.

Tobin has everything: successful business, good social standing, beautiful home, and a young girlfriend. Yet he gambles extravagantly for even more money, and when it cannot be obtained legally, searches for illegal funds to be even more rich.