The arrival of Francis's new bride on Hal's birthday sparks a fray that drives the younger siblings out---and into a posh hotel.

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

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.

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.

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. The good news is, Dewey's not around. The bad news is, his baby sitter is Lois's annoying co-worker Craig. Meanwhile, Hal and his very pregnant wife are off at a romantic retreat---feuding.

Hal and the boys offer to watch baby Jamie so an exhausted Lois can finally get some sleep. Hal leaves the boys in charge while he goes to the Lucky Aid to pick up more diapers. While the boys are watching Jamie, three beautiful teenage girls arrive and woo Malcolm, Reese and Stevie away for the night, leaving Dewey alone with the baby. Meanwhile at the Lucky Aid, Hal doesn't have enough money for the diapers and Craig forces him to work. Back at home, Dewey concocts an elaborate bedtime story for Jamie involving each member of his family.

Malcolm chooses Reese as his subject for an Abnormal Psychology mid-term project; Dewey earns some extra cash as a street performer.

Neighbors have the annual "The Wilkersons are gone" block party until they come home early. Reese and Dewey set up a plan to get money by letting Reese-tortured kids get revenge. Hal and Lois enter a kielbasa-eating contest and Malcolm unknowingly assists a robbery, but a surprising twist comes in the end.