Amos Decker witnesses an execution-style murder outside FBI headquarters, but his team can find absolutely no connection between the shooter and the victim, nor a hint of any possible motive for the attack. Harper Brown, an agent of the Defense Intelligence Agency (DIA), orders Decker to back off the case. The DIA believes solving the murder is now a matter of national security because information may have been leaked to a hostile government or terrorist group-- and an attack may be imminent. Forced into an alliance with Agent Brown, Decker remains focused solving the case before it's too late.