Too often with a series aimed at young readers the author uses up all his good ideas (and his funniest jokes!) in book one, and then just "mails-in" the following books in the series. Not so with the Doctor Proctor books...at least not so far. "Bubble" surpasses the silliness of the first Fart Powder book but is also more complicated plot-wise, more layered in it's humour, and even manages to raise a few moral issues when your not looking. Apparently Nesbo was just warming up with the first book - or perhaps he was conscious that the kids who read and liked the first book would be a year more sophisticated, and he wrote this one for a slightly older audience. Whatever. I loved it.