Everyone in Germany should be cautious during war time, as the enemy may be listening. The Kettwig family, who owns an armament factory, should be especially careful as they are closely watched by those who want to obtain the secret weapons produced at their plant, such as an advanced anti-aircraft wire. They should be suspicious of everyone around them, including Nolte the waiter and potential romantic interests. The Kettwigs and their employees are a valuable target for the enemy.