Lois and Hal leave the boys with Francis for the weekend, promising that, if all goes well, Francis may not have to go back to military school. However, mayhem ensues and Malcolm requires hospitalisation.
On Monday morning, Malcolm and his brothers convince their ailing mother that it's Sunday.
When the family takes a vacation to a casino, Hal is banned from gambling and takes Malcolm and Reese on an ill-fated trek into the desert. Meanwhile, Lois and Dewey win a free day of spa pampering and Francis spends a lonely weekend at home.
Malcolm gets into trouble with an elderly neighbour, Francis's slacker friend enrols at Marlin Academy, and Dewey trades his backpack for a purse.
Malcolm tries to help Reese bring his grades up, while Francis is exiled to a friend's house after defying Lois's order to patch the roof.