What is the main conflict in Stephen Coonts' Deep Black by Stephen Coonts?

The book opens with Charles Dean and his partner, Tommy Karr, riding separately on a bus and seeing a beautiful woman being robbed. Both run to help the woman. Tommy catches the thief and returns the purse to the woman. Tommy and Charles decide to have coffee while waiting for their afternoon meeting.

After this, the action of the book begins to explode. The two men work for the National Security Agency in Deep Black, a highly secret covert operations division that uses the most advanced technology in the world. The two men are on their way to a meeting, but before they meet their contact in the park, he is shot in front of them. The only problem is, he wasn't their real contact.