This was the first of the long-running German "krimi" series based on the mysteries of Edgar Wallace (actually, there were two simultaneous series from rival companies, the other based on the works of the author's son Bryan). As Tim Lucas and other astute critics have pointed out, the films were the precursors of the Italian giallos and ultimately the slasher pictures of the 70s and 80s. They also have obvious stylistic links to the superhero and superspy action genres of the 60s.
Most of the key elements of the series already appear in this effort -- the foggy Soho underworld settings; the cabaret shows (which became progressively sleazier); the archvillain with his bizarre modus operandi and grotesque henchmen; the clever, persevering but underappreciated Scotland Yard inspector; the flippant comic antics of Eddie Arent (here appearing as the consummate English butler with Kato leanings) who is always smarter than he seems; the statuesque ingenues; the unfathomable plots featuring dozens of red herrings; and the quite violent-for-the-time stalk-and-murder sequences. Later the series would rely more on flashy camera tricks and tongue-in-cheek stylistics (especially under Alfred Vohrer's nifty direction), but here the proceedings are mainly played straight. Harald Reinl's work was always atmospheric but rather stiff in its mise-en-scene and ragged in continuity. However, this film features quite a sadistic, eye-opening ending that seems to have wandered in from a Jess Franco opus. Well worth a look, especially for amateur film historians.