There's not much to recommend here, really. A good cast does not a good spy movie make. Rather, this plays like a late-cycle Edgar Wallace krimi with the Scotland Yard detective a secret agent and a murderer who happens to have stolen a top secret invention. The circus milieu (the Palladium in Vienna) is quite tedious but other Vienna locations are nice to look at like the empty amusement park where the villain hides out.
Pierre Brice is Philippe Taylor (changed from `Tissot' for the English dub apparently) an agent on the trail of the device. Brice was a looker who made a lot of westerns in the sixties and he was in the anthology Spy Against the World (66) but most may recognize him from Mill of the Stone Women (60). He's very bland here but that suits the rest of the film.
The score by Charly Niessen (arrangements by Gert Wilden), is okay but is occasionally inappropriate for the action on the screen. Director Alfred Weidenmann can't do much with this material either; the script is just plain weak. I had high hopes for this one but you can skip it knowing you haven't missed a darn thing.