499761 Megamonster by David Walliams

On a volcanic island, in the middle of shark-infested waters, stands The Cruel School. The lessons are ludicrous, the school dinners are disgusting and the teachers are terrifying. When Larker is sent to the school, she quickly realises that VERY odd things are going on involving sinister Science teacher Doctor Doktur, a secret cave and a ‘Monsterfication Machine’. Can Larker unravel the teacher’s wicked plot?