Mrs. MacGrady is diagnosed with cancer and the kids react differently. Arthur and D.W. rush to her support, Francine is scared, and Muffy is initially unaware of the symptoms, but jumps to action when she realizes how to help. Lance Armstrong guest stars as himself for the second time.
George wonders whether anyone would notice if he just disappeared, and so vows not to speak until someone notices him. Of course, his friends do notice, and they decide to cheer him up with a surprise party.
Fern volunteers to help an elderly neighbour, Tony Wu, with his household chores, and then discovers his past life as a Kung Fu celebrity. Suddenly she imagines herself as his student, and she will soon be a Kung Fu master herself! But will she be disappointed to learn that dish cleaning and laundry folding are not really part of some special martial arts training? Or can she learn a valuable lesson in acceptance and friendship?
Buster finds a piece of paper with names of his classmates and numbers beside them. He, Arthur, and Francine believe it's a class ranking system based on behavior, and Francine tries to find ways to have a higher rank.
Francine and the Brain are competing for Student of the Month. He is in the lead and Muffy wants her to win. Francine and Muffy frame him into doing a bad deed, so Francine becomes Student of the Month. They continue to frame other students in fear of being caught from their first plan.
Binky introduces Emily into wrestling when he babysits her. Her personality changes from being nice and polite to being loud and rough. He changes her back to her normal self when she begins to hurt other children in result of her behavior.
The final volume of the Henry Skreever series, "The Knights of the Bouillabaisse", is released at last. Prunella and Marina compete to see who will be first to finish it, but they soon learn that speed reading does not always pay off.
George meets a new friend named Carl, who has Asperger's syndrome—a form of autism. George is unsure about how to act around him, but the Brain helps put autism in perspective for him so he can understand some of Carl's mannerisms.
Arthur, Sue Ellen, and Binky find a woodland oasis near their homes and vow to keep it a secret. Soon they start to find evidence of human habitation and wonder if they've discovered an ancient civilization.
Fern and Muffy start a greeting card business. Muffy paints the covers and Fern writes the poems. All the work makes Fern lose interest in writing, so she tries to figure out how to get make it interesting again.
To boost school pride, Arthur and his classmates form the Lakewood Pride Committee, which seems to pressure and brainwash students to have pride for their school. Sue Ellen and the Brain don't join the group and are accused of not loving their school.
Arthur is dismayed when he learns that the energy drink endorsed by Dark Bunny, his favorite superhero, is unhealthy. He goes in search for a new superhero who doesn't sell out from their principles, and ends up making his own named Supernova.