From friendly but helpless Canada had come the false feint at America's mighty, steel-armored line. Investigating that strange attack, Operator 5 learned that to save his country from the most astounding invasion in history, he and his volunteer aides must cross the sea to fight a desperate undercover battle with the three bandit nations of the Old World-and, man for man, match American agents against their foes in the grim hope that he might overwhelm a ruthless enemy!