As Myrtle's sister, Catherine considers herself very knowledgable about the affair between Myrtle and Tom, and takes great delight in sharing the inner workings of the relationship with Nick.
Catherine joins Nick on the couch in the New York City apartment Tom and Myrtle use for their entertaining and proceeds to monopolize his attention, as she relates her opinions about the affair.
"Neither of them can stand the person they're married to." "Can't they?" "Can't stand them...If I was them I'd get a divorce and get married to each other right away."
As Catherine continues to talk, it becomes apparent that she doesn't hesitate to voice her opinions about her sister's situation, and that Catherine doesn't always have accurate information for a basis to her opinions. For example, she blames Daisy's Catholic faith for preventing Tom from getting a divorce, but Nick knows that Daisy is not Catholic.