Against Peggy's wishes, Frank secretly helps design a set for a musical in which Timmy is performing. Feeling jealous of all the positive attention Frank is getting for his work, Timmy devises a plan which forces Frank to admit his involvement on set, but Timmy's scheming backfires. Meanwhile, Mike grows increasingly concerned that Joey is heading down a shady moral path with all his wheeling and dealing, and decides to teach him a lesson.
The Cleary boys beg Peggy to tell them she loves them, so Peggy posts a ranked list of their names on the fridge in the hopes that someone will divulge who broke the dining room light fixture. Timmy incriminates his brother but feels so guilty that he gets a horrible stomachache and heads to the hospital. Back at home, Mike invites Grover, a co-worker, disguised as an amateur detective to their home to help compel a confession out of the guilty Cleary child.
Mike and Peggy think they might be expecting again, but later Peggy is diagnosed with having a cyst instead. Meanwhile, the kids spy on Mike and Peggy to try to figure out what their unusual behavior is about. When Pat overhears that they are going to have a little sister, the Cleary kids decide to dig deeper.
To hide a mess Eddie made, his girlfriend, Wendi, tries to distract Peggy by insisting she take a day off with a fun day out while they take care of the housework. To everyone's surprise, Peggy accepts the offer and requests Wendi tag along, with the ulterior motive of teaching her a lesson. Meanwhile, Eddie enlists the help of his brothers to clean up and keep Mike out of the house while Wendi and Peggy are out.
Lawrence, the prodigal eldest Cleary son, returns home from the seminary and breaks the news to his family that he’s dropping out for good, leaving Mike and Peggy upset and wondering why. Meanwhile, Timmy decides he wants to audition for a children’s theatre production but when Peggy finds out where it’s being held she forbids him from participating. Elsewhere, Eddie tries to keep his girlfriend a secret after Frank finds out and tries to blackmail him.