The children are looking forward to going on holiday with Bill and Allison, but Bill is instructed by Sir George to guard the future prince of Tauri-Hessia. Unknown to Bill, his car has been fitted with a tracking device by a man working for the sinister Madame Tatiosa, the wife of the Prime Minister of Tauri-Hessia, who wishes to kidnap the present king and place the puppet prince on the throne.
