S6E23: The Springfield Connection

In "The Springfield Connection," Marge becomes a police officer after experiencing a thrilling chase with a criminal. She quickly gets into the swing of things, but her new role creates tension at home, especially with Homer, who can't resist breaking the law even under his own roof. Homer gets involved in an illegal blackjack game in the garage, unaware that Marge is onto him. When she discovers what's going on, she arrests her own husband, but he manages to escape the legal consequences, as usual. The real kicker comes when Marge faces off against Herman, the ringleader of the operation. He tries to eliminate Marge to keep her quiet, but she uses her police training and some good old-fashioned luck to take him down. By the end of the episode, Marge is disillusioned with police work and returns to her regular life, leaving Homer to grumble about losing his garage to a police raid.