All Paris trembled with terror as those mystery shells blasted the city. Planes searched the clouds for a lurking Zeppelin - but found nothing. Up at the Front, the sky was black--there was no fire to indicate a long-range gun. What was it that was smashing Paris - killing women and children - threatening to destroy the nerve center of the whole Allied forces? The Front waited in horror while G-8 and his two sky buddies set out to tackle this invisible menace on fighting death wings!