Schooldays at St Clare's are never dull for twins Pat and Isabel O'Sullivan in Enid Blyton's much-loved boarding school series.

In book nine the unimaginable has happened - the twins made head girl! It's a tough job - cheeky first formers and cruel Priscilla keep the girls on their toes.

It's the twins last year and there definitely will be mischief!

Between 1941 and 1946, Enid Blyton wrote six novels set at St Clare's. Books 5, 6 and 9 are authorised sequels of the series written by Pamela Cox and feature storylines set in between the original Blyton novels. These books were published in 2000/2008 and are unillustrated.