Designated Survivor, Paperback/John H. Matthews

The United States Capitol is overtaken by terrorists during the State of the Union speech and the nation's leadership are held hostage. Precautions are taken for such an extreme event. One cabinet member is chosen by the president to be away from the Capitol and D.C. This is the Designated Survivor. An elite NSA operator and his team are called in to aid in their rescue and to track down the people responsible.