The year is 1960, a time before computers when television is a strange new invention. It is school holidays, it is pouring with rain and nine-year-old Emma is bored.
Then something exciting happens. In her toy cupboard, Emma finds an old wand she once made at school. Pretending to be a wizard casting spells, she discovers that the wand really works! It turns her cat, Penny, into a girl. Now Penny says she knows all about magic. Her mum knew a cat who knew a witch's cat, you see. She thinks being a girl will be fun, but she is still a cat inside and only remembers spells that would be useful to cats.
Emma learns that being able to do magic with Penny's help can be a lot of trouble, especially when Penny sometimes behaves more like a cat than a human. Their unfriendly neighbour, Mr Blight, who hates cats, is accidentally turned into a zebra that runs off down the street.
Emma and Penny go through one adventure after another, some dangerous, some funny, as they try to find him and make him human again. This tests Emma's resilience as well as the friendship she has with best friend, Lizzie.
Despite all the challenges she faces, Emma always gets home safely. Mr Blight is made human again, Penny is turned back into a cat and Emma's friendship with Lizzie becomes even stronger.