This 1940 film takes place in Germany during the Second World War.  The family Kettwig, which runs an armaments factory, is constantly inventing new contraptions to defend Germany against enemy attack.  At this time, their engineers develop a special wire, which when attached to balloons, will be the most effective anti-aircraft device to date.  Of course, enemy agents are always on the prowl for information about how successful the Kettwig family has been at developing this new wire.  A waiter, Nolte, is introduced to enemy agents by another disloyal German.  He is recruited to spy on the Kettwigs.  At the same time, a pretty spy is sent to seduce the young Bernd Kettwig while his secretary is wooed by a very handsome gentleman, who is, you guessed it, a spy.