Petula is Molly's black pet pug. She was once owned by Miss Agnes Adderstone and was grumpy, spoilt and always fed chocolate chip cookies. Molly hypnotized her and Petula became Molly's pet. In various books, Petula has learned to hypnotize. She has the ability to hyponotize others. She hypnotized two sleepy mice in California in the second book. In the third book, Petula stopped time. Most significantly, Petula helped Molly gain entrance into the mind machine room by hypnotizing Miss Cribbins' evil pet, Taramasalata.
In the second book, Petula starred in a movie while they were in LA, and in the fifth book, she set out to find Molly in London with two other dogs. When Molly morphed into another dog, she and Petula got to know one another. Petula has saved Molly's life on various occasions.