The Bolds are visited by Fred's mother, Granny Imamu. She's travelled all the way from the Serengeti, she does not approve of what she finds: hyenas, living as people! Granny Imamu starts to stir up mischief with the twins, encouraging them to get in touch with their beastly side at school.
And then the twins' teacher comes to the Bolds with a rather unusual problem: her grown-up son Jeffrey just isn't like other people. He's rather hairy, doesn't much like to talk, and loves to monkey about. If animals can become people, could it happen the other way around . . . ?