Enemy of the state : a Mitch Rapp novel
(Book)

"After 9/11, the United States made one of the most secretive and dangerous deals in its history. The evidence against the powerful Saudis who coordinated the attack would be buried. In return, King Faisal would promise to keep the oil flowing and deal with the conspirators in his midst. When the king's own nephew is discovered funding ISIS, the president suspects that the Saudis never intended to live up to their agreement. He decides that the royalty needs to be sent a message and that Mitch Rapp is just the man to deliver it. The catch? America can't be seen moving against an ally. Rapp will be on his own. Forced to make a decision that will change his life forever, Rapp quits the CIA and assembles a group of independent contractors to eliminate the threat." --,(Source of summary not specified)