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.

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.

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.

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.

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.

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.

Hal, Reese, Malcolm, and Dewey go into business selling Christmas trees, with the boys using some of their own money, but two priests send homeless people to their business, trying to sabotage their sale.

Malcolm alerts the A.C.L.U. when he encounters censorship working on the high-school literary magazine; Hal tries to flirt with the woman in his office responsible for cutbacks.

Jamie's babysitter coerces Malcolm into doing a "small" task for her; Dewey finds a friend, only to lose him to Reese; Francis persuades Otto to confront an old adversary that once courted Gretchen.