This particular episode was written by Teri Hatcher herself.
High school reeked - at least for one of Lois's old classmates, who hatches a diabolical plot for revenge.
Lois has to attend her high school reunion and Clark accompanies her as her fiance. There, she learns that two (and later a third one) of her former classmates' spouses have disappeared and she decides to investigate those disappearances to find out what happened.
While investigating, something strange starts happening to Clark; he is slowly shrinking. Clark goes to Dr. Klein as Superman, who runs some tests to find out what caused this.
The clues that Lois finds lead her to one of her former classmates, cosmetics designer Annette Westman.
Annette wanted revenge on all those who mistreated her in high school, so she created a shampoo with a secret formula that causes people and things to shrink into miniatures so her friends would run to her for comfort, but she really wanted to see how they were suffering.
When Lois confronts her, Annette tries to kill Lois then shrink her as well. But with the help of Superman, Lois gets away and Annette accidentally pours the entire formula onto herself, causing her to shrink away to nothing. Dr. Klein finds the antidote and everyone returns to their original size.