The Demon Headmaster Strikes Again — Gillian Cross

Dinah, Lloyd and Harvey hoped they'd seen the last of the Demon Headmaster when they moved to a new village. However, almost immediately, they can tell something's not right about the place. There's a loud buzzing noise coming from the biogenetic research centre, and a creeper that grows
extraordinarily fast. Why are the security guards so scary? And why does everybody in the village use exactly the same words to describe the research centre? Dinah becomes even more suspicious when someone pretending to be a doctor comes to their house, and manages to trick them into giving DNA
samples . . .

With the help of their new friend, Simon, the children investigate and find a way into the building. Inside, they discover a huge egg. Hatching from it is the result of an experiment conducted using Dinah's DNA - an experiment that is the work of the Demon Headmaster.

This time, he's determined that no one will stand in the way of his plans!

'this will be greatly enjoyed'
Books for Keeps