A baleful limping man walks through Prague. He is Asmodeus (Juraj Herz), the fiend of lustfulness, entertaining himself by putting together by magic couples of lovers. He only fails at the swimming pool. Zuzana (Jana Sulcová), the good-looking blonde, ignores the men whom the devil foists off onto her. She loves Honza (Václav Neckár) and the boy shares her feelings. The fiend is annoyed by the couple and tries to provoke a row. He sends heavy rain to force them into a hotel and then warns Zuzana's father by phone, but the young lovers manage to get out in time. Then the obstinate Asmodeus takes Honza in his sleep to the Institute for Emotional Disorders, where he shows him the ugly sides of love - hysteria, voyeurism, fetishism, suicide attempts...