Lois and Hal are spending the weekend at a family wedding, leaving Francis -- home for a visit -- in charge. When Malcolm overhears them discussing whether Francis has spent long enough at the military academy, he enlists his brothers in a scheme to get Francis home by preventing any of the usual disasters. But three of Francis's dude buddies turn up to party and trash the house, and while frantically cleaning up Malcolm gets a serious head injury that necessitates the usual trip to the emergency ward. How to prevent Mom and Dad from finding out? Enter Caroline, who has begged Malcolm to look on her not just as his teacher but also as his "friend" -- a declaration that costs her $400 in medical bills. Meanwhile, Hal and Lois discover that his family has a new nickname for her: "Lois Common Denominator." Her humiliation provokes Hal to declare his devotion to her -- and the snooty bride and groom discover that their honeymoon car is already being put to use.... Home again, Mom and Dad a