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.

A sociohistorical drama about the construction of the Simplon-tunnel: A conflict develops when German workers want to strike and fight for better working conditions while Italian workers simply want to earn money and provide for their families.