When we first meet Cassandra, she seems to be simply a young maiden, presumably in a mill town in Industrial England.
She applies for a position with an innocent virginal Professor, and slowly she seduces him, for the benefit of his lovely Assistant. By the end of the second week she has opened the Professor's life to the pleasures of the flesh, and his lovely Assistant.
So there we are in the professor's private quarters where the Assistant has just spent some time seducing her lover, the Prof, and is in the process of organizing her and Cassandra's love life with the Professor.
I feel the Short Story was written with a tongue in cheek but is up there with much longer stories.