Jennifer Aniston finally breaks with her Friends image in her portrayal of Justine, a 30-ish depressed, bored store clerk working at Retail Rodeo. Justine is married to a big, lump of a man Phil (John C. Reilly). She gave up any idea of higher education after high-school to marry Phil. He's a house painter by day, glued to the hip of this vapid co-worker Bubba (Tim Blake Nelson). They paint by day, come home and get stoned, and stay glued to the TV all night. 

Justine works at the cosmetic counter and is bored out of her brains. She's not the only one. Cheryl (Zooey Deschanel) makes some hilarious, insulting and very rude announcements over the PA system (nobody really notices) until she is re-assigned a less potentially damaging role of working with Justine at the make-up counter. Take one look at her make-up and run. Instead she advises a gullible patron that the spectacularly awful make-over she has just given her is "all the rage with the Frenchies".

It's no wonder that Justine is intrigued and attracted to a new young clerk named Holden, who is curiously enough reading Catcher in the Rye. As they become closer Holden explains to Justine that Tom is his slave name (given to him by his parents, with whom he still lives!). He is a writer and is very very different from Justine's usual co-workers. 

Justine and Holden begin a passionate affair which Bubba finds out about. He blackmails her into having sex with him, or else he will tell her husband Phil. Silly Justine, she should have known better. Better that Bubba so adores Phil he never would have told him the truth. Now a greater problem arises when Justine finds herself pregnant.

I won't say more because it would give away too much of the plot, but I will say that The Good Girl allows it's characters a wide range of emotional possiblity and expression, and the final scene between husband and wife is a fitting end to a very good 'small' movie.