This is the film that made Marlene Dietrich famous. A conservative old professor is taken in by the charms of a cabaret singer and is so mesmerized by her that he gives her his money, and spends so much time in the cabaret that his students spy on him and ridicule him, and his career as a professor comes to a bad end.
The fact that he gets in a fight with a sea captain over the singer and turns to drink also helps his career to its quick end. Just to be near her, he eventually joins her group and plays a clown in her show, being routinely humiliated as part of the act. The film ends with his – well, we can’t give away the entire story but this is a true classic.