No one's saying this boisterous sitcom has to slow down with age. But Malcolm's 100th episode hurts itself by hopping from story line to story line instead of sticking with the strong central situation.
Lois (Jane Kaczmarek) is primed for battle when her sister Susan (guest star Laurie Metcalf) comes to visit. Barbed remarks soon lead to outright screaming over grievance No. 1: Hal (Bryan Cranston) dumped Susan for future wife Lois—on Susan's prom night, no less. When Lois discovers that Susan needs a kidney transplant, the question becomes whether they can call a truce while there's still time. The show deserves credit for resolving the situation without losing its characteristic irreverence.
Too bad the episode keeps cutting away to the boys' piddling problems. Malcolm (Frankie Muniz) and Reese (Justin Berfield) can't use the cool car they got from Susan because Hal removed the engine. Dewey (Erik Per Sullivan) makes way too much cotton candy. And, in a laughless side trip, oldest brother Francis (Christopher Masterson) guides a group of rebellious little girls on a scout trip in the desert. Some children should be neither seen nor heard.