Lois and Hal leave the boys alone for the weekend with Francis. the boys assume that if all goes well, Francis may not have to go back to military school.

The whole family attends a Krelboyne family picnic, and Malcolm dreads his performance in the event's Academic Circus will make him look like a freak. Disasters abound as stage acts bomb, families feud, and Malcolm's dad serves meat to vegetarians.

The boys stay home from school when their mother thinks it's Sunday instead of Monday. Malcolm thinks of a plan to get Francis out of trouble once again. Hal gets sucked in by a Porsche dealership.

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

Hal feels like his job is a piece of c* after going to Dewey's class for parent job day. So he decides to take a "kidney failure" weeks off. While Francis is forced to work at the lucky aid over spring break.

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

A negative job-performance review riles Lois; hoops play with the boys energizes Hal; a vermin infestation busies rat-killer Francis.

Highway horror: Reese gets a learner's permit, which he promptly proceeds to abuse by commandeering a driving-school vehicle.

Dewey rules, thanks to his new dog that intimidates Malcolm and Reese; Hal and Lois hit the town with big plans---and flu symptoms.

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. Elsewhere, Reese butts heads with a goat; and Malcolm and Dewey take a tumble into a tiger den. Another storyline checks in on ne'er-do-well Francis, now the unlikely foreman of a dude ranch owned by a cheery German businessman.

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.

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.

When Dewey's pet rabbit does good in a state contest, the family must travel to Las Vegas for the nationals. But Reese unknowingly sells the rabbit to a restaurant. Now it is up to Dewey (with a little help from a "choking" Reese) to try and save the rabbit.

Meanwhile, Malcolm tells Hal and Lois that they embarras him, and that is why he didn't tell them he won state science honors. As a form of repayment, Malcolm gets great seats for him and Lois to see Lois' favorite singer. Lois then gets lucky and is invited backstage where all she really wants to do is figure out why Malcolm doesn't want her around.

Hal, on the other hand, is looking all across Las Vegas for a slot machine that he has had dreams of winning the jackpot on.

Francis is also in trouble when he gets behind on duties at the ranch, and for the first time sees that Otto isn't just a pushover for everything.

Reese continues to be a great soldier in the Army until he finds himself in a situation where his Sergeant cannot help. But after comparing being captured to being grounded, he takes action and leads his team to victory. But being such a successful soldier has it's bad parts as well, as Reese prepares to jump from the plane - right into Afghanistan. Malcolm has his hands full as well as he attempts to prove Hal innocent. But being good with numbers helps as Malcolm notices all of the prosecutions given dates are on Fridays - which Hal hasn't worked on in over 15 years. And with Reese missing and Hal's case, Lois falls deeper and deeper into insanity.