A masked killer is murdering the pimps, prostitutes and drug addicts of Milan, and leaving a dragonfly ornament on each corpse. Paul Naschy is the police inspector trying to stop him.
As far as giallos go, this is unremarkable stuff. The murders are unconvincing at best, and laughable at worst. There are far too many scenes of chases which showcase very lame gunfire. The plot constantly throws distractions at you like a coat button, a tattoo, golf clubs, extra marital affairs, and two deadly fairground rides, but they don't add up to an engaging story. Paul Naschy does a decent job as the detective, although I couldn't stop staring at his ridiculous comb-over (actually all the male characters in the cast have terrible hair),but most of the rest of the acting is wooden. Even Erica Blanc, who has made striking appearances in other movies, does not impress. To cap it off, the climax is very weak.
Currently quite hard to see on DVD and Bluray, this movie has not aged well. Groovy theme music and early 1970's fashions aside, it does not have a lot to recommend seeking it out.