On a visit to Francis' dude ranch Hal can't help being disappointed in Francis' success, Reese and Malcolm fear Francis has turned into an overly responsible grownup, and Gretchen punishes Dewey for breaking a valuable doll.

Malcolm skips out on Thanksgiving to go to a party; Reese becomes abusive to Hal and Dewey as he attempts to prepare Thanksgiving dinner.

Lois' younger sister, Susan, pays the family a visit and brings with her expensive gifts for the boys, biting remarks for Lois and a cold shoulder for Hal – whom she has never forgiven for dumping her for Lois. Lois and Susan's competitive relationship takes a turn for the worse when Susan gives Malcolm and Reese her prize '65 Mustang convertible. But when Lois discovers that Susan needs a kidney transplant, she puts her anger aside and offers to donate her kidney to Susan, which Susan only sees as the perfect opportunity for Lois to one-up her.

Malcolm convinces Dewey to do poorly on an I.Q. test, so that he won't become a ridiculed Krelboyne student. But Dewey does so badly that he is placed in a class for the emotionally disturbed. Hal and Craig compete in a dance competition.

When Hal and the garbageman get into a trash-dumping war (which benefits Dewey more than anyone else), Hal enlists Reese's help. Meanwhile, Lois gets her job back at Lucky Aide (off probation), and fights against Malcolm in order to take down an offensive billboard of a smiling black janitor (whose nametag reads "Slappy") holding a mop and a 6-pack of malt liquor. Soon it's an all-out war between mom and son - until Lois encounters a fellow employee who is more racist than the billboard.

Hal is sleepless because of their upcoming 20th wedding anniversary. So he ask Reese for some ideas for presents. Then Reese gets the idea to brainwash his dad while he's nervous. Dewey's friends are set up in an upcoming student body election when a bully nominated two of his geeky friends. Malcolm takes up playing the electric guitar, though Lois discourages his musical ability. He writes a heart warming song. When he plays & sings his creation, Dewey figures out that his song is sung to the tune of the "Meow Mix" jingle!

After Hal forbids Dewey from inviting his peculiar classmate Chad over for a sleepover, Dewey quickly finds out that his father had good reason to warm him. Meanwhile, Malcolm and Reese find out that they are not as popular as they once thought, then plot "revenge" on their classmates.

When Hal decides to attend his first annual Neighborhood Association meeting with Malcolm, he is strongly encouraged to take on the role of President. Being his dad's right-hand man, Malcolm sees a perfect opportunity to add some excitement to the community, while Hal's agenda is a little bit different. Meanwhile, Francis takes on a new job as a camp activities coordinator and turns to Dewey for his input on some creative new games. While Dewey revels in his afternoon of fun, his fed-up classmates take their teacher, principal and janitor hostage.

Unbeknownst to Lois, the boys enter her in the Mrs. Tri-County Pageant as a joke. When they overhear the other contestants remarking that Lois doesn't have a chance of winning, they plot to help their mother take the crown. Meanwhile, Malcolm is blackmailed into delivering love notes to a contestant for Herkabe, and Reese discovers that, according to the Mrs. Tri-County Pageant manual's scientific formula, he is beautiful.

Reese and Malcolm try to perform the ultimate Halloween prank.

Lois discovers she has mono after a visit to the doctor. She then ends up giving it to Malcolm after her maternal instincts begin. As a result, both Lois and Malcolm are forced to spend an entire day and night together in the same room. Hal, meanwhile, is invited to all of his neighbors' parties after they know Lois will not be attending any of them.

For the senior prom, Reese gets paid to take Janine, a studious girl in class, but only after she gives him a makeover and sends him to finishing school, while Malcolm aligns with the unpopular kids to form an anti-prom they call "Morp." Unfortunately, while Malcolm and his friends protest the official dance, they don't know how to make their "Morp" exciting. Meanwhile, Dewey discovers there aren't any childhood pictures of him, so he concocts an elaborate scavenger hunt to punish Hal and Lois.