Lisa is heartbroken when her career test reveals her ideal future occupation--homemaker." Bart's test shows that he should be a policeman. Lisa is determined to prove her test wrong. She goes to a music teacher to get his opinion. He informs her that, having inherited her father's stubby fingers, she can never be a very good saxophone player. Bart rides along with officers Lou and Eddie to see what it's like being a cop.

Her dreams shattered, Lisa loses interest in being a good student. When Principal Skinner discovers Bart's new interest in law enforcement, he enlists him as a hall monitor. Soon, Bart has order restored to the school.

After being punished for sassing Miss Hoover, Lisa steals the teachers' editions of the schoolbooks. Baert tracks down the thief, locker by locker. When he discovers that Lisa has stolen the books, he takes the rap for her. He is stripped of his hall monitor sash and is given 600 days detention. Thankful to her brother, Lisa plays her saxophone outside his classroom as he serves his time.