Brain falls in love with Billie who is a female mouse that lives in another cage in the lab. Brain dresses up and tries to impress her with his intellect, but she seems more interested in Pinky's sense of humor. Pinky, however, is not interested. He already has a girlfriend named Phar FigNewton. Pinky then offers advice to Brain. Brain begins to have some success, but Billie is changed into a super-intelligent mouse by an experiment. Brain becomes worried that Billie will take over the world before he can.