Jolly Foul Play by Robin Stevens

Daisy Wells and Hazel Wong have returned to Deepdean for a new school term, but nothing is the same. There’s a new Head Girl, Elizabeth Hurst, and a team of Prefects – and these bullying Big Girls are certainly not good eggs. Then, after the fireworks display on Bonfire Night, Elizabeth is found – murdered. Many girls at Deepdean had reason to hate Elizabeth, but who might have committed such foul play? Could the murder be linked to the secrets and scandals, scribbled on scraps of paper, that are suddenly appearing around the school? And with their own friendship falling to pieces, how will Daisy and Hazel solve this mystery?