The leader of a gang of spies Zarnoff (Irving Pichel) manages to escape his own execution thanks to a rare and exotic drug and continues his plan to blow up an ammunition convoy using a robot controlled bomb.
Tracy manages to foil his plan but Zarnoff remains on the loose and determined to wreak havoc and avenge himself on Tracy.
As it is a serial (and thus originally shown in short chunks of around fifteen minutes each) the action is fast moving with regular cliff hangers. The need for regular cliff hangers does make the plot a bit contrived and repetitive of course when watched in a single chunk.
It is a bit of a strange Dick Tracy story - in fact it is hardly Dick Tracy at all in many ways. There is no Tess Truehart in this tale for example but he does have a secretary called Gwen (Jennifer Jones).
