The Circus of Adventure by Enid Blyton

Who is the strange, pompous foreign boy Gustavus Barmilevo invited to the children's home by Bill for the holidays? The children soon discover that he is a prince, named Aloysius Gramondie, and has enemies on his trail. The enemies want to overthrow his uncle, who is too strong a ruler for them, and place the prince on the throne as a puppet ruler. Jack and Kiki find themselves following the others, who are kidnapped and taken to the strange country of Tauri Hessia; but he finds help with a circus. Will Jack be able to rescue the others with the help of his new friends and decide the fate of an entire nation?