The Major Crimes Unit is called to a scene that looks like a home invasion gone bad. An old woman, Mary Conrad, was murdered and there are groceries all over the floor. Provenza is convinced it's a follow-home robbery but no one believes him. He also thinks the victim looks familiar. She appears to be a former cop, Mary Conrad.
Sharon remembers Mary well, as she investigated her as an IAB agent and Mary wasn't very nice to her. Mary had been involved in fraud while on the job and didn't think she was doing anything wrong.
The cops quickly learn that Mary had been shoplifting groceries and whatnot and the cops let it go because she was an old lady. They also learn that she poisoned her neighbor's dog.
The landlord tells them about a large guy named Dustin who is on parole and who had issues with Mary. Naturally Dustin, like all idiot suspects, tries to outrun Major Crimes when they confront him at his home. He ends up crashing into a trailer and needing medical attention.
Dustin turns out to have had nothing to do with the crime after all that, leaving the detectives back at square one. They realize that whoever killed Mary was hiding in her home. Their attention again turns to the landlord, but he claims not to be the only one with a key. Eventually, the detectives learn that the husband of Mary's niece killed her because she was letting them support her financially while secretly getting a pension and she wouldn't give the money back so they could send their son to Georgetown.
Meanwhile, Ricky shows up and announces Sharon's engagement in front of the squad, then gets to work on getting Andy's marriage annulled so Sharon can have a church wedding.