A cloak and dagger chase set in Austria, this is a thriller in a new setting. Peter and Bobbie Hadley were thrilled to be allowed to accompany their sister Eileen when she accepts an invitation to study in Vienna. Charles Grant, curator of a museum, is to escort them. But they have hardly left England when trouble starts. A newspaper report states that Dr. Barova, a Hungarian scientist, has fled to Austria with his wife and son -- and the picture published indicates the boy is a double for Bobbie Hadley. Bobby is kidnapped in a case of mistaken identity -- and the pursuit of his captors brings Peter into a circus where the Barova boy and Bobbie are hidden. Brisk bravado here, well written.