The film tells the love story of two young couples. According to their social ranks, construction worker Edy is dating employee Siegi, while medical student Dieter is dating art school student Sonja. Rather unintentionally, they exchange partners. During a carnival ball, Dieter makes out with Siegi because he falls for her her fresh and happy girlish manner. Sonja coolly observes this game and sees this intermezzo as a test for their relationship. While Siegi and Dieter vacation at the sea, Sonja falls in love with Edy. Now the die seems to be cast for new constellations. But when both couples stand in front of the registrar’s office, they finally come to their senses.
At the end of the 1950s, the production of optics in the German Democratic Republic has reached top quality and instigates interest in the West. When national demand rises strongly and at the same time the export to South America heavily decreases, the Volkspolizei - the GDR police force - starts to look into the case. Two seemingly unrelated cases are the starting point for the investigation by second lieutenant Schellenberg of the department for optics racketeering: An old woman who was arrested in the Berlin city railway for trying to smuggle a pair of binoculars to West Berlin, and a dead person in an area of allotments who was involved in obscure dealings with optical devices.
