A severe teacher who one night goes to "El Ángel Azul", a notorious cabaret, to take his students from there, who come to the place seduced by the charms of the singer Lola-Lola. However, Professor Rath, a 50-year-old bachelor, ends up falling into the networks of the cabaret. From then on, his life will be a descent into the hells of humiliation and moral degradation.