The Cook approaches the young couple, although the audience cannot see her. The Girl discusses the fact that she is in charge of the housekeeping, since her mother is ill. She talks about the fact that the Cook is a fat and ungainly woman, from the Hummel family of vampires. "She is eating us," the Girl says, adding that she will not leave the house, and that she extracts all the nourishment from the food that she serves.
"What an extraordinary house! It is bewitched," the Student observes, as the Cook comes in and grins broadly at them and leaves on her own time. The Girl tells the Student not to be impatient, adding that they also have a housemaid that they have to clean up after. She tells him that the room they are in is called "the room of ordeals," because it has many defects, and the Girl must clean up after the servants regularly.
The Student wants to make music, but the Girl insists that first they must complete "the labor of keeping the dirt of life at a distance." The Student wants to marry the Girl, but she insists that that is impossible. When the Student remembers that she dropped her bracelet out the window, presumably for him, she clarifies that it was because her hand has grown so thin.
The Cook enters with a Japanese bottle, and tells the young couple, "You drain us of sap, and we drain you. We take the blood and leave you the water, but colored...colored. I am going now, but all the same I shall stay, as long as I please." She exits.
The Student tells the Girl that he went to the Old Man's funeral the other day and cried. He recounts that he saw a man who stood at the head of the coffin who was in love with the Old Man's son, and that "the dead man had borrowed money from his son's admirer." He then tells her that his father died in an asylum, taken there after speaking his mind recklessly at a dinner party that he hosted.
The Student launches into a monologue about how life is full of illusions, saying, "Where is anything that fulfills its promise? In my imagination." He becomes disillusioned, picking up the harp, which now makes no sound, and realizes that the vampire's poison is beginning to affect him. "Saviour of the world, save us! We perish," he calls out, as the Girl begins to die. Bengtsson enters, and the Girl tells him to bring the death-screen.
As the Girl dies, the Student asks the Buddha to give him patience and purity of will. As "the strings of the harp hum softly and a white light fills the room," the Student repeats the recitation that he gave before.
The final stage direction reads, "The room disappears. Bocklin's picture The Island of the Dead is seen in the distance, and from the island comes music, soft, sweet, and melancholy."
Even if the Old Man disappears before the beginning of the last scene, his influence continues to reverberate in the house, as the Cook is from the Hummel family and is just as vampiric as he was. The Girl describes the curious process by which the Cook steals away the good elements of their food in the kitchen: "She boils the nourishment out of the meat and gives us the fibre and water, while she drinks the stock herself. And when there's a roast, she first boils out the marrow, eats the gravy and drinks the juices herself. Everything she touches loses its savor." Through some strange reverse alchemy, the Hummels are able to extract the good qualities from nourishment for themselves, an apt metaphor for greedy money-lending.
Soon enough, we learn that even though the existence of the Student and the Girl in the Hyacinth Room appears idyllic and picturesque, it is actually a "room of ordeals," appearing beautiful, but "full of defects." The beauty of the room masks a number of horrible qualities that the innocent youths must endure, that have largely to do with the reversal of the master-servant relationship. The wealthy young woman must do the work that her servants do not do, and look after the messes they make, rather than the other way around.
The extra labor that the Girl must do to make up for the negligent servants prevents her from living the artistic and pleasure-filled life of an aristocrat. This gets enacted literally when the Student wants to play music with her, but she insists that they must complete "the labor of keeping the dirt of life at a distance." In the world of the play, wealth cannot afford individuals the pleasures of a more leisurely life, because the servants do not do their jobs. In staging such a dynamic, Strindberg examines the choreography of class antagonism, in which the ruling classes get to live pleasurable lives while the servants tidy everything in their wake.
The play is thus a kind of symbolic meditation on the nature of inequality in the world. The peasant class strives for what the ruling classes have, while the ruling classes struggle to maintain their dominion over what is theirs. No one is satisfied; rather they recede into a kind of stagnating pattern, in which this power struggle is never resolved or redeemed. Through the innocent figures of the Student and the Girl, we have foils to this struggle, too idealistic characters who hope for the best, even if they are already beginning to become corrupted by these inequities.
The Student, who was filled with promise and potential, is left, at the end of the play, with a rather defeated and disillusioned view of things. He asks himself, "Where is beauty to be found? In nature, and in my own mind, when it is in its Sunday clothes. Where are honor and faith? In fairy-tales and children's fancies. Where is anything that fulfills its promise? In my imagination." He realizes that the world is damned, and that he is powerless to change it, before asking for help from some unknown "Savior." In this state of disempowerment, the Student also imagines a reality that might save him, one in which the Buddha will "grant us patience in our ordeal and purity of will, so that this hope may not be confounded."