When the family goes to a water park for a day, Dewey is left home with an elderly, stern babysitter. Francis is hustled at pocket billiards by his military-school commandant.

Hal, Loi, Malcolm and Reese are trapped in a horrendous traffic jam. Francis enters himself in a bet that recalls the egg-eating wager in "Cool Hand Luke." Malcolm becomes smitten over a girl he meets. Dewey has his own little adventure--all over the world--before his family returns home.

Shenanigans abound at the fancy spot where the family's dining with the Kenarbans, and at Francis' school, where rowdy teenage girls are partying.

A family weekend vacation to a casino turns into an ordeal in the desert for Hal, Reese and Malcolm, who wander onto an artillery range. Francis sneaks home, but has no one to play with.

Hal and Lois heads off to a convention while the boys stays home for the babysitter. Malcolm, Reese and Dewey assumed it's just another old woman, their parents hired to watch them. They decide to do a series of pranks on their babysitter, which includes the covered up sewer tank with a blanket and a book for the old woman sit on. To their surprise, their babysitter is a hot, teen-aged girl named Patty. She is sweet to them, but also bitter because she was rejected by Francis, a long time ago, because she was obese. Now the boys compete against each other to see who will prove their eldest brother wrong in his rejection and sleep with her without sex. Meanwhile at the convention, Lois tries in vain to stop the fight between Hal and Jack, who stole his idea.

Malcolm's humiliation as a Krelboyne drives him crazy, so he fakes his way into seeing the school's shrink, with whom the con continues.

Malcolm gets a role in the high school play and is so captivated by high school gossip that he forgets his lines. Lois discovers the joys of massage. Hal and Dewey build a society of model buildings in the living room. Francis tries to show his individualism at school when the commandant cracks down on personal belongings.

Reese, promising champion of his school's wrestling team, gets beaten by a girl, completely demoralizing him. So he gives up his school-bully carrier, which destabilizes the natural order of things at school. Francis tries to get out of academy at his birthday in an attempt to avoid academy-birthday-traditions.

Dewey starts carrying a purse to school. Francis's friend Richie joins him at military school. Malcolm becomes a slave to an old woman in the neighborhood.

Lois' estranged parents, Ida and Victor, pay the family a visit. Right away, trouble starts brewing. Victor bonds with Reese, Ida gets Malcolm into a fight, and Dewey is haunted by childhood memories of his inattentive grandparents.

Lois gets a traffic ticket and immediately blames Francis and makes him get the money to her. To do this, Francis stages a stunt for the other cadets' amusement. Malcolm finds evidence that Lois was wrong about the traffic ticket.

Lois forbids the boys to ride a motorbike they found, but Reese disobeys and breaks a leg.