Budapest in the thirties. The restaurant owner Laszlo hires the pianist András to play in his restaurant. Both men fall in love with the beautiful waitress Ilona who inspires András to his only composition. His song of Gloomy Sunday is, at first, loved and then feared, for its melancholic melody triggers off a chain of suicides. The fragile balance of the erotic ménage à trois is sent off kilter when the German Hans goes and falls in love with Ilona as well.

A medical doctor who is regarded as a specialist in retort research has been found dead. Science journalist Vera Pukall investigates the alleged suicide and uncovers the ruthless activities of a large pharmaceutical company. She receives help from Dr. Svoboda, of all people, the group's main stockholder.