Jack Reagan, a former attorney from New York, is visiting Washington, D.C. for his best friend's wedding. While taking a walk through Rock Creek Park on an unseasonably warm January day, he stumbles across a terrorist attack connected to the desertion of Marine Lance Corporal Lawrence Eggerton in Afghanistan several months earlier. Reagan comes to the aid of the federal agents and schoolchildren under fire, taking decisive and lethal action against the attackers. As he is interviewed about the shootings, Reagan's accounting of his actions and his analysis of events impress the Acting Director of the Naval Criminal Investigative Service, Francis Smythe, who decides on the spur of the moment to grant Reagan's request to look over some information concerning Eggerton. Smythe and Reagan both believe that the shooting in Rock Creek Park is part of a larger terrorist plot, and with Smythe's support, Reagan's participation in the investigation grows as he helps uncover information that points to other terrorist cells operating within America. As the investigation progresses, Reagan develops an increasingly close relationship with a talented young investigator, Special Agent Amanda Watson. Reagan and Watson utilize the combined resources of NCIS and the FBI to track down the terrorists, aided as well by Reagan's longtime friends in the special operations community who are separately tracking Stinger missiles that disappeared during an arms transfer in Benghazi. In a fast-paced story spanning from Afghanistan to Argentina and from the frozen tides off the New Jersey coast to the warm waters of South Beach, Reagan's mysterious past is gradually revealed as he and his friends race against an unseen clock to prevent a devastating series of terrorist attacks with weapons the likes of which have never before been used on American soil.