Lucy advertises for a roommate to help with the expenses, and after reading the correspondence, she finally decides on Carol Bradford (Carol Burnet), a frumpy off-kilter librarian. Carol soon starts taking over, reorganizing the apartment, laughing like a hyena, and generally driving Lucy nuts. Lucy and Mary Jane scheme to help Carol develop a social life (to keep her out of Lucy's hair), so they have a small party to introduce her to some boys. It isn't long before usually mild-mannered Carol begins drinking, singing, and being the life of the party.