Mona, a self-reliant record executive, is set to move into the penthouse apartment that her father has promised her. Her plans come to an end when she learns her spoiled half-sister, Dee Dee, lay claim to the same apartment.
Dee Dee attempts to get closer to Mona by planning a joint birthday party. Meanwhile, Dee Dee unwittingly reveals that Phyllis lied to Mona about things that have shaped her world view since she was a child.
When Mona gets on Dee Dee's case about leading a privileged existence, Dee Dee decides to prove to her and herself that she can survive in the real world by landing a job at a waitress. Meanwhile Phyllis encourages Mona to go to a dating service to find a good man .