Malcolm, whose frenetic home life is a kind of zoo, begins the fourth season by accompanying his family to the real thing. A visit to the zoo offers close encounters with creatures great and small. But Hal wishes he could have passed on an encounter with Lois's former beau, who lectures on rain-forest animals

High school's first day vexes Malcolm, who acquires an unfortunate nickname; and Hal, a parental "volunteer" running afoul of authority

Christopher Lloyd adds to his gallery of eccentric characters, playing Hal's quirky, cranky and very wealthy father, Walter, in this rollicking episode. The occasion is a birthday celebration for the old man, but the snooty female in-laws seem more interested in offending Lois. Their shabby behavior initially goes unnoticed by Hal, who's desperately trying to bond with his self-centered dad; and by Dewey and Reese, who seek some of Grampa's dough by currying favor with him

Acting dumb like Reese eases Malcolm's stress and lands him a date with the new light of his life, an attractive girl who's really a dim bulb

Brotherly love is lost on Malcolm and Reese, now out to sabotage his sibling's birthday in devilish strikes met with crafty counterattacks

Malcolm starts to date Nikki. Meanwhile, Hal and Lois must take abstinence pills in an attempt to be better parents. At the ranch, Otto is furious with the other ranchers who keep destroying the fence that Francis is building to keep the cattle inside

After joining the basketball team at school, Malcolm soon finds himself under the coach's skin due to his constant complaining, which eventually gets him kicked off the team. Determined to put an end to his horrible habit of talking before he thinks, Malcolm starts "holding his tongue" which solves all the problems with his coach, girlfriend, and parents, but it ends up causing more stress than before. Meanwhile, Hal takes up speed walking and is desperate to be the best while Reese gets Craig to take him and Allison to a concert and almost ruins his date

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

Grandma Ida is even nastier than usual (if that's possible) because of a tumble down the front steps that resulted in a broken collarbone, prompting her to sue her daughter and son-in-law for pain and suffering. And there's more momentous news on the home front: Lois is pregnant

After being rattled by a battle among the boys, a pregnant Lois ponders the consequences of raising another brawling kid. So she fantasizes that her unruly sons have morphed into well-behaved young daughters. Malcolm becomes Mallory, Reese is transformed into Renee and Dewey turns into Daisy

A sex lecture from Lois rattles Malcolm; a ranch calamity unnerves Francis; disharmony among Hal's music group is a prelude to their concert. Also, a day in jail tests a defiant Reese, who faces a "Scared Straight" encounter

After Lois is out of town, Malcolm and Hal got into a fight leading Malcolm to get expelled from his house. Malcolm lives with his girlfriend in her attic, as Hal put signs for "Missing Malcolm."

Jessica, a sly, 16-year-old sitter outfoxes the boys while Lois is away and Hal's busy with a second job as a whiz of a salesman

Malcolm tries to emancipate Dabney from his overbearing mother while Hal invites his ne'er-do-well old buddy to the house. At the ranch, Francis is forced to share a room with Otto

A garage sale that's entrusted to Reese (yikes!) yields treasures near and dear, like Hal's old radio transmitter, which he makes operational. And a PC dating back to 1976 that Malcolm plans to sell to Craig for $1300

An academic competition faces the Krelboynes in an event Malcolm derides. Especially when he learns his teacher has a cheating plan. Also: a commitment to a formal dance ruffles Reese, who's now trying to ditch his date

Hal and Lois are penning their will, and think back to all the trouble their sons put them through. It is there that Lois' problems with Francis are finally revealed and how her inability to admit when she is wrong lead to a lot of the problems the family has been dealing with

When Hal and Lois go out of town for a "last chance" getaway before the baby comes, Reese has a big bash that gets out of hand. College-age thugs show up, cancel the party and set up a drug-making operation in the garage. All Reese and Malcolm can do is knuckle under

Leonard, a cynical, genius chess player with no friends or job, makes Malcolm think he could grow into a similar adulthood. Determined to prevent this undesirable fate, Malcolm tries to help Leonard change his life by lining him up for a job interview with the obnoxious Craig. Meanwhile, Francis finds employ as a nude model and begins to delight in the exposure

Lois goes into labor while Hal and the boys are at a bridal exposition. Ida moves in after her apartment burns down and she refuses to stay with Susan.Dewey reveals the date his parents chose for the baby's planned delivery is his birthday in an announcement at the exposition to humiliate Hal

While Lois is in labor, the house is hectic, and Hal, desperate to get home, has crashed the car on the way out of the expo

With the arrival of their fifth child, Lois and Hal search for a "creative" daycare solution