Amanda Applewood is not particularly keen on riding, and she's certainly not keen on using up her valuable holidays joining the Lockett family for a riding competition. Jill, on the other hand, would love it. Amanda suggests Jill take her place, on her perfect pony, Plum. It seems like utter heaven to Jill, until she arrives at the Locketts' and finds Amanda hasn't actually told them Jill is going in her place ... They think she's Amanda. And they don't like Amanda. Jill is so furious with Amanda she decides she'll pretend to be her and make sure the Locketts carry on not liking Amanda.

Not only does Jill have the Locketts to contend with, she also has to get used to Plum, whom she's never ridden before, and compete with the Locketts in just two weeks' time.