For Philip, Dinah, Jack and Lucy-Ann, it seems a real bore to have the strangely conceited young foreign boy, Gussy, staying with them for the Easter holidays. But Gussy, it turns out, is more than he seems — and he and the other children are soon in grave danger. Caught up in a sinister political plot in the kingdom of Tauri-Hessia, they must find a way to outwit the villains and restore justice to the country — with the help of their new friends, the folk of a travelling circus!