Tired of A.J. being a suck-up to Mr. Crocker and getting good grades for it, Timmy wishes that he was the teacher's pet, but Poof turns him into Mr. Crocker's guinea pig. The problem worsens because Mr. Crocker is going to use guinea pig Timmy for his experiment, which is a genetic hybrid of different animals that create the ultimate Fairy-catching monster.

After being rejected yet again by Trixie, Timmy seeks help from Cupid, only to find he is unavailable as he is on vacation. Therefore, Timmy takes Cupid's bows and arrows and entrusts Cosmo into the temporary role of Cupid so he can make Trixie fall in love with him. Unfortunately, Cosmo messes everything up again by missing his shots and hitting the wrong targets, and soon Cosmo and Wanda, Mr. Turner and a dead rosebush, Mrs. Turner and Mr. Crocker are head over heels in love for each other. When Trixie is finally hit with the arrows and falls in love with Timmy, he realizes now has to save his mother before she becomes the new Mrs. Crocker.