Jess and her twin brother Matt are planning their birthday - but they can't agree on what sort of party to have. Finally they settle on a disco, but Jess isn't too keen on all Matt's friends coming! He's asked the whole class, so she feels she should do the same - even if that includes school boff, Becky. The only problem is, now Becky thinks Jess is her new best friend. When Jess goes shopping for an outfit for the party with her friends, they bump into Becky, who tags along and insists on buying the same things as Jess. Then the DJ that Jess's mum has booked for the party falls through at short notice - the whole thing looks like it's going to be a disaster... But between them, the Party Girls rise to the challenge!