 The war lords of a potential enemy of the US has the spy ring,led by John Baroda, the Spy King (John Merton) and his aide Nitra (Eve Whitney), sabotaging the plans for a vast defense system of radar stations along the American borders. Radar Defense Bureau operative Chris Calvert (Kirk Alyn) comes to the rescue of a brilliant radar scientist, Joan Hughes (Jean Dean), who has been kidnapped by Baroda henchmen in chapter 1 ("The Fatal Fog"), and the two battle together before putting an end to the Spy King in the aptly-named chapter 12, "Day of Reckoning."