When Professor Popper starts his great experiment in the school laboratory no one knows quite how it will end, but it gives Simon, his young assistant, a shrinking feeling ...

Will Professor Crabbit discover what has happened to his old friend Professor Popper and his young assistant Simon? And who are the two mysterious strangers?

Will the two strangers steal the formula? And how can the professor and Simon escape?

The Professor now has more problems. Will Elizabeth be able to get help and find the antidote to the shrinking pills?

How can the professor and his friends escape from the two mysterious strangers?

How can Elizabeth find a way to save the Professor and her school friends from the two crooks?