The gang causes havoc when they all go to the zoo.
When his parents volunteer during his first day of high school, Malcolm's dream of losing his "geek" image quickly vanishes.
Hal's father has a birthday party and they attend. Dewey and Reese try to ingratiate themselves to the wealthy relative while the whole extended family gives Lois the cold shoulder.
Malcolm enlists his brother Reese's help when he wants to play dumb to impress a girl.
Keeping with tradition, Malcolm and Reese play practical jokes on each other until Lois grounds for his birthday.
Malcolm has to keep his relationship with a girl a secret from her Vietnam veteran father.
In an effort to get along better with people, specifically a basketball coach who doesn't enjoy Malcolm's lip, Malcolm keeps his mouth shut. His father tries to be the fastest walker in town.
Expecting Francis to be mischievous as they are, the boys are disappointed when he doesn't turn out to be so. They take it upon themselves to prove that he is, as he always was, as much a pest as they are.
After a fall on their property, Grandma Ida sues Lois and Hal. Compounding the monetary concern, Lois learns that she's pregnant.
Lois lives out her fantasy of having four girls and not boys.
Reece spends time in jail in an effort to curb his raucous behavior. Malcolm is freaked out when Lois decides to talk to him about sex.
A confrontation between Hal and Malcolm sends Malcolm packing and Hal panicking over his missing boy.
When Hal starts his second job at a stereo store, the boys are outraged to find out their sitter is the same age as Malcolm. Meanwhile, Hal ends up partying with his coworkers... who happen to be half his age. Francis tries to cover for allowing an adult film to be shot at the ranch.
With Lois away, Hal decides to play with his friend Larry, who Lois won't allow in their house. After spending time together, Hal starts to realize why. Malcolm and Stevie try to goad Dabney into taking a stand against his controlling mother.
Reese's garage sale leadership is questioned by the other boys. Hal finds his college radio equipment and puts his pirate radio show on the airwaves.
Malcolm has to deal with an academic competition and the teacher who wants the team to cheat. Meanwhile, Reese thinks of ways to avoid taking Alison to a dance.
Hal and Lois reflect on the boys' misbehavior as they prepare both their wills and themselves for the upcoming addition to the family.
When their parents leave them home alone, Reese decides to throw a party which quickly escalates beyond the boys' control.
Malcolm sympathizes with a lonely chess genius and tries to help change his life for the better in the hope that he won't befall such a future.
To give Lois some alone time, Hal takes the boys out. He thinks they're headcing for a car show, but finds he's stumbled upon a bridal show. With nothing else to do, they stay and get into various degrees of trouble. Lois is greated at home by her mother and, at the peak of frustration, her water breaks.
Hal fights against numerous odds, including injury, to try and be at Lois's side as she gives birth to the newest member of their household.
Lois and Hal masquerade as members of a church to gain access to the day care program for their newborn baby. The boys have to put up with sunday school to aid their parents.