The only double the producers could find for Christopher Lee was the circus' real lion tamer, who Lee described as being "half my height". In order to make the situation credible, 6'4" Lee was shot in close-up, so the height differential would not be too obvious to the audience. According to Lee, he wore a black mask through 90% of the movie anyway.
Barberini's circus' winter quarters were largely filmed in Winkfield, Berkshire, the real-life home of Billy Smart's circus, one of Britain's most famous circus companies.
The 1967 US release was in black-and-white and edited down to one hour and five minutes for bookings on the lower half of the bill.
Though shot in color, the film was released in Germany in black-and-white. Rialto Film, the production company of the German Edgar Wallace series, was very close to Constantin Film, this movie's German distributor and co-producer. Rialto wanted to promote a production of its own as the "first Edgar Wallace film in color". That was Der Bucklige von Soho (1966), released in Germany only a couple of months after this film. The original color version was released in Germany on DVD in 2006, though in edited form.
Although presented as a British production, it has the look and feel of a German krimi film. The cast includes veteran German actors Heinz Drache, Eddii Arent and Klaus Kinski. The story was based on an uncredited book by Edgar Wallace whose stories were the basis of many of the German krimi films being produced in that era. This was a British-German co-production that even had an uncredited separate director that handled the German version.