The novel begins with Mildred Hubble and the upcoming traditional assembly where all of the first-years are given their own black cats that they will teach to ride on their broomsticks with them. Unlike the other girls, who receive black kittens, Mildred receives a tabby cat, which she simply calls Tabby. The kitten is unable to sit on a broomstick, so Mildred carries Tabby in her bag. Miss Hardbroom disapproves and Mildred has to stop. Afterwards, another witch called Ethel Hallow teases Mildred about it, and dares her to turn her into a frog. Mildred loses her temper and turns Ethel into a pig instead.