Appropriate Sanctions — Michael Grant

Life is good for Paul Ducane. He's happily married with a promising career as a political science professor and consultant. But all that changes when his bright young graduate student, Jeff Levin, hacks into a government computer and downloads a file from a mysterious organization called the National Internal Affairs Agency. Immediately, the order goes out: get that file back and take “appropriate sanctions” against anyone in possession of it. Before Levin realizes that the file contains explosive information capable of bringing down the president of the United States, he is assassinated. Ducane, now in possession of the file, becomes a hunted man as well.
Desperate to evade his pursuers, who have the capability of tracking his every move by monitoring credit card usage and cell phone calls, Ducane flees into the bowels of the the New York City subway system. Beaten by muggers, he is helped by an enigmatic homeless woman who teaches him the arcane ways of the “tunnel people” who inhabit the city's underground. His situation gets worse when the police wrongly accuse him of murdering Levin. Now he must evade not only his pursuers, but the police as well. Still, he knows he can't hide indefinitely. He must get the file to the senator who is investigating the president's administration.
This is a page-turning thriller that delves into shadow governments, assassination, duplicity, and questionable friendships.