After discovering something terrible in the nuclear power plant, Waylon Smithers bribes Carl to keep what he has found quiet by giving him tickets to a Bob Seger rock concert. He invites Homer to join him, and he leaves Marge to chaperone a field trip on a World War II battleship, to her dismay.
At the field trip, Marge pairs up with the seemingly-boring Sarah Wiggum. After the latter sneakily tricks the children into going to bed early, Marge realizes that Sarah is not who she seems and is hiding her boisterous personality from the other mothers. The two are soon kidnapped after spending all night together, and Marge and Sarah find themselves in the lair of two women that Sarah surprisingly used to thrive with.
The other burglars, Erin and Bette, explain how, while they and Sarah were heisting a museum where Chief Clancy Wiggum was on duty, the fourth member of their team - Lindsay Naegle - betrayed them and had them arrested. However, Sarah was spared the fate due to falling in love and having slept with Chief Wiggum. They plot to steal the Hourglass Diamond from their betrayer and Marge turns out to be useful in the planning, so they recruit her for the heist.
They execute the heist perfectly until Naegle realizes she has been robbed. Naegle calls the police, and when they arrive, Homer and Wiggum instead apologize to their wives. While attempting to stop Marge and Sarah herself, she ends up tumbling down the long amount of stairs, allowing Marge and Sarah to escape publicly with the jewel, much to the surprise of Patty and Selma and their friends back at the Simpson house.
This episode turned out to be a one off thing (non canon) due to show runner Matt Selman answering people's tweets (Tweet since deleted) regarding why Sarah got a different voice in this episode and why she was portrayed like this, as well as why did nothing about her make sense regarding this ex criminal stuff. He said "everything and nothing is canon" as well as the fact they changed her voice for this episode for the story and plot line to work, implying that if Sarah's original voice actor Palma Hayden voiced her for this episode, it wouldn't work because true Sarah isn't this Awkward quiet weirdo who can't piece two words together, to this all the sudden cool chick that was a former sexpot robber with other 2 one off throw away characters minus Naegle.
He also later confirmed more openly and clearly on an IGN article in regards to episodes such as this and others being set in their own universe and are not apart of the actual universe of the show and the already established timeline and or personality of a character, as well as his support for a Hit and Run Remake.