Amos Decker witnesses a murder just outside FBI headquarters. A man shoots a woman execution-style on a crowded sidewalk, then turns the gun on himself. Decker and his team can find absolutely no connection between the shooter and his victim. Enter Harper Brown. An agent of the Defense Intelligence Agency, she orders Decker to back off the case. The murder is part of an open DIA investigation, one so classified that Decker and his team aren't cleared for it. But they learn that the DIA believes solving the murder is now a matter of urgent national security. Critical information may have been leaked to a hostile government --- or worse, an international terrorist group --- and an attack may be imminent.