Diane is asked to be a judge at the outset of this episode. But as the hour drags on, she learns of a corrupt judge and helps the firm bring him down. This doesn't sit very well with the powerful people that wanted to get Diane elected, and they eventually withdraw their support.
It was a solid use of Christine Baranski, as well as a nice spotlight for the character.
The storyline of the immoral judge actually brought together everyone on the show. Alicia first brought the issue to Diane's attention after a nine-year old client of her was unfairly sentenced by him. This led to an investigation by Cary and Kalinda into his past... which resulted in evidence of an assault on his ex-wife... which prompted Will - a friend of the judge's - to dig deeper and realize that his pal had arranged for pay-offs in exchange for sending kids to a detention center.
It's always nice to see storylines and characters intersect in this way. Everyone at the firm played a key role on the episode and each actor shined.
On the homefront, Grace befriended a girl at school whose father is also in prison. Turns out, Peter sent him there; unfairly, the girl's mother claims. This accusation leads to a great scene in which Jackie sprays the woman with a hose for accusing her son of such an unethical act. Grace and this new friend video chat near the end of the episode, though, remaining close despite their family feud.