Homer was sentenced to Community Service, and ended up delivering Meals On Wheels. When he went to Mrs. Bellamy's house, she was holding an ax when she greeted him, frightening Homer.
It turned out that Mrs. Bellamy was just a kindly old woman starved for company, and the ax was for cutting Meals On Wheels steak. Homer helped Mrs. Bellamy with a couple of household chores, and this quickly escalated into his being at her house all the time.
Marge went over to complain, and ended up helping Mrs. Bellamy as well. Soon Homer and Marge were, in effect, Mrs. Bellamy's personal servants.
Both of them, but especially Marge, came to resent this, particularly when Mrs. Bellamy gave them degrading chores to do and generally treated them poorly.
After a card game with her friends, Mrs. Bellamy was apparently stabbed with scissors by a man with braces and a necklace was stolen from her house.
Marge and Homer were arrested, tried, convicted, and sentenced to death for Mrs. Bellamy's murder. Just before their execution date, Homer confessed to everything so that Marge could live.
When Homer was strapped into the electric chair and the switch was pulled, it was revealed that all along they had been on Frame Up, a reality TV show.
Mrs. Bellamy wasn't dead, and wasn't even an old woman; she was really actress Carmen Electra in disguise.