The Muggle-Wump in this story has a wife and children and is subject to animal cruelty at the hands of Mr and Mrs Twit, who are retired circus trainers.
Assisted by the Roly-Poly Bird, who arrives while on holiday in England, and who can speak both the African language of the monkeys and the English of the native birds, the Muggle-Wumps rescue the latter and escape from their cage while the Twits are away.