Martin's globetrotting sister suddenly arrives in New York and visits Martin at his office. Martin informs Eddie of Susan's return, and he asks Eddie to show Susan the city. Eddie has almost no problem with this request. Eddie and Susan have been dating for eight years, and Eddie is nervous about letting Martin become aware of their relationship. Susan prefers letting Martin in on the secret, and lets the cat out of the bag by not returning to Martin's apartment (where she was supposed to be staying). Martin still sees his sister as a young girl and cannot accept that she can take care of herself, especially with noted ladies man Eddie Charles. Martin and Eddie have a falling out over this issue, and Susan refuses to be treated like a little girl.

Martin's sister Susan wants to get married in a small ceremony without the family knowing. Nevertheless, the whole family ends up getting involved, planning a big wedding party.