William 'dressed as a Red Indian, cooking an experimental mixture of treacle and lemonade in an old sardine can'; William escaping from a wrathful shopkeeper by pretending to be a window dummy...William's long-suffering parents might not agree, but there is no doubt that for William these are Happy Days indeed.

Robert has very strong reasons for wanting William to be kept away from a particular fancy dress party. This is the eleventh book about the irrepressible Just William.