Dinah and her brothers are pretty sure they're rid of the Demon Headmaster once and for all. When people start dismantling the research centre Dinah contacts Professor Claudia Rowe, who's an expert on artificial intelligence. With Dinah's help she saves some of the precious materials and they become friends. Then weird things start to happen. Libraries start closing and their books are taken away. Telephones stop working, and there is no internet access. People start talking like robots - even Claudia Rowe - and more and more of them seem to be wearing strange green hand badges. It all adds up to one thing: the Demon Headmaster must be back. Dinah's search leads her to the university where she finds him developing a Hyper-brain - a computer with superhuman intelligence and deadly potential. Suddenly she's trapped. Is there any way to foil his plan?