Based on the classic film, Mary is a party girl who lives it up in New York clubs and is always on the social scene, to a point where all patrons at her favorite bar greet her by clinking their glasses. After getting arrested for illegally charging people to come to a party, wild and reckless party girl Mary (played by Christine Taylor) calls upon her godmother Judy (played by Swoosie Kurtz) to bail her out. However, Judy wants Mary to start taking some responsibility in life instead of aimlessly partying for the rest of her days, much like Mary's deceased mother did. Judy then talks Mary into taking a job as a library clerk as a means of proving herself to be responsible.
Most of Mary's friends think the job is something Mary shouldn't even consider staying with, though they realize she's up to the challenge of getting herself together. She is put to the test by snarky and stuck up library assistant Wanda (played by Merrin Dungey) doubts Mary and believes her to be just a party girl. After a stressful first day, Mary is ready to quit and gives up hope. However, her friends Derrick (played by John Cameron Mitchell) and Oneal (played by Matt Borlenghi) help her master the Dewey Decimal System and she becomes a literal overnight wiz.
Judy has some initial doubts about Mary's fast learning skills and considers firing her. Mary further impresses Judy by finally breaking through to Judy's introverted ESL students, decides to keep her at the library, much to Wanda's dismay. Mary, pleased to be able to have Judy respect her, decides to continue her partying ways at night, so long as she can manage the pace of a nine to five job each morning.