The play begins with a Student entering the stage, which depicts a street outside the fancy townhouse of a Colonel. The Student approaches a water fountain and asks the Milkmaid standing nearby for a cup of water. He has had a sleepless night, after acting heroically the previous night at the site of a collapsing house in town.
Nearby, the Old Man, Jacob Hummel, tells the Student he has been reading of his heroics in the newspaper. Hummel knows the Student's father from his days of money lending. The Student deduces that the Old Man is the lender who ruined his father financially, but the Old Man insists that it was the other way around. The Old Man then tells the Student to go to The Valkyrie that afternoon to listen to the opera, promising that if he sits next to the Colonel at the opera, he will get inside the Colonel's townhouse and win favor with the Colonel's daughter, referred to in the script as the Girl.
The Student does as he's told and gets invited into the home of the Colonel, where he spends time with the Young Lady in her Hyacinth Room (a room filled with hyacinths). Mysteriously, Hummel also manages to infiltrate the home and seeks a meeting with the Colonel. During their meeting, Hummel convinces the Colonel that he is not a nobleman, nor a Colonel, and must hand over everything he has. The Colonel's wife, who over the years of living in a small closet has turned into a Mummy, comes into the room. She is the former lover of Hummel and together they parented the Girl. At the ghost supper that they host in their house, the Mummy reveals that Hummel is a notorious usurer and a vampire of sorts. In the course of the dinner, he dies.
In the final scene of the play, the Student and the Girl are seen together in the Hyacinth Room. The Student wants to marry the Girl, but she says they have to wait. When the Cook appears, the Girl tells the Student that she drains all of the nutrition from the food and also the life from everyone in the house. She is related to Hummel and has a similarly vampiric relationship to the world. In the midst of telling this tale, the Girl dies and the Student is left alone in the house, where he asks for a more hopeful future.