For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
The curtains open, and we find the narrator worrying about the fact that Robert, his wife's blind friend, is coming to spend the night. In the process, he reveals his assumptions about blind people. He also thinks about his wife's first marriage, her suicide attempt before her divorce, and her relationship with Robert. His wife tells him about Robert's life with his wife, Beulah, who recently died of cancer.
Act II
This act opens with Robert's arrival. It includes the somewhat awkward before-dinner conversation, the devouring of dinner, and the marijuana smoking after dinner. Drinks are served and consumed throughout the act. The curtains close on the woman falling asleep on the couch between her husband and Robert.
Act III
This act is all about cathedrals. The narrator tires to describe a cathedral to Robert but fails. Robert suggests a nonverbal approach. With Robert's hand on his, the narrator begins drawing a cathedral. Soon, Robert asks the narrator to close his eyes. The curtains close on the finished drawing, and on the narrator's closed eyes.