In A Doll's House, Dr Rank is a close friend of the Helmer's who has been secretly in love with Nora all these years. He has a disease which is slowly killing him and he knows that his time is now limited. He is discussing the evening's entertainment and suggests that Nora should go to the next "masquerade' as a good fairy and "she has simply to wear her everyday dress," such is her goodness.
Dr Rank says he will be invisible at the next dance: "There's a big black hat — haven't you heard of the invisible hat." He is apparently suggesting that he will not actually be at the next dance as his illness will have killed him. He, like Torvald, feels that parents' actions are detrimental upon their children and their indiscretions bring suffering. "My poor innocent spine must do penance for my father's wild oats." Nora is most distressed at this thought as she believes her "secret' will then corrupt her children.