The film begins with a faceless man (technically a man with a face, but one which is obscured to us) being chased by police in Paris. He tries to elude them by scaling the Eiffel Tower, suggesting that he's thrown in the towel mentally. The man leaps to his death (in a hideously poor matte(i) effect so bad they show it twice in the first 3 minutes of the film), and we flash back to see how things ended up this way.
A no-good jewel thief, Antoine Gottvalles, sneaks into a Parisian brothel, from which he's been barred. The mistress, Madam Colette, agrees to let him sample her wares one final time. Unfortunately, Antoine's preferred prostitute, Francine, is found beaten to death minutes later. Antoine is convicted of her murder and sentenced to death, swearing vengeance from beyond the grave before he's led from the dock. He escapes as he's being transferred between prisons, only to be decapitated when his stolen motorbike crashes into a parked truck. Just when you think it's safe to return to the brothel, though, someone begins dispatching prostitutes and judges willy nilly. Has Antoine returned from beyond the grave to act upon his dying promise? This is a giallo not a supernatural film, so no, he hasn't. But who is doing the murders? And will we see that terrible matte effect one final time before the credits roll? (Yes, we will.)
Oh, and there's also the small matter of the investigating officer, Inspector Fontaine, being a dead ringer for Humphrey Bogart. This is no accident; he's played by Bogart professional lookalike Robert Sacchi (known from Play it Again, Sam). This explains one of the film's alternate titles, The Bogey Man. Somehow, the ostensible presence of Humphrey Bogart in the film never becomes too distracting; indeed, the film as a whole has a strange off-kilter vibe, and after a while you just accept each bizarre digression as par for the course.
This may explain how three of the main protagonists, Howard Vernon's* Professor Waldemar, his daughter and her frustrated lover (his assistant) slot neatly into the film after about twenty minutes, despite having no real connection with the events we've seen until that point (OR DO THEY??). Waldemar is friends with the judge who sent Antoine down, and they discuss the case over wine and chess, but such a tenuous connection to the events which are at the centre of the plot hardly justifies the amount of screen time afforded the judge's friend, his daughter and her lover (OR DOES IT??).
This leads us back to Inspector Fontaine. Ordinarily, you'd assume that such a gimmicky character, and one who is in a natural position to drive an investigation, will be anointed chief protagonist. He makes a belated play for such a role about halfway through, when he suddenly starts asking hard questions and refusing to let people leave before at least a couple of "Just a minute" and "Oh, just one more thing"s. This, though, is one of those films where no-one really grabs hold of the narrative, probably because the narrative itself is paper thin. Everything of note plot-wise is condensed into about five minutes towards the end of the film; the rest of the time we jump back and forth between various characters and scenes, the strangeness of which only really strikes you upon reflection.
Take the scene where Rosalba Neri (playing Antoine's ex-wife) sings her new song in her boyfriend Pepi's nightclub, as he watches on. Pepi is distracted by muscly peplum stalwart Gordon Mitchell, who's drunkenly pawing at Tina, a blonde girl who floats through the film seemingly with one purpose, to antagonise Neri. Pepi improbably beats up Mitchell, whose bulging shirt appears about to burst open at any moment, and saves Tina from a public sexual assault. Neri's only response is to throw a hissy fit, accusing Pepi of having only eyes for Tina and ignoring her own chanteusing. Even by the haughty standards of giallo characters, that's damn cold.
There are also some 'interesting' experiments with colour. And by 'interesting', I mean 'failed'. Most of the murder scenes feature the decisive blow repeated several times, with the image tinted a different colour for each repetition accompanied by a sting on the soundtrack. This may have been an attempt by the editor (hello, Bruno Mattei!) to liven up some pedestrian directing. At least it's different, I suppose. Then there's the moment when Antoine swears vengeance from the dock, when the image suddenly becomes solarised. This is also different, very different. And there's a reason why other directors don't use solarisation in their films.
The director here, Ferdinando Merighi, barely made anything else. He actually does a solid job for the most part, from a technical point of view (dodgy murders and solarisation aside). In terms of constructing a top-tier giallo, though, he fails miserably. The plot is weak, there are too many characters being juggled, and the stylistic flourishes which a top giallo demands are vastly misjudged (again, this may well have been Mattei's doing, but, if so, at least he was trying to bring some style to the party). On the plus side, the cast is surprisingly impressive (although sadly Barbara Bouchet and Rosalba Neri are kept studiously apart), and you get to see what it would have been like if Humphrey Bogart lost most of his charm and acted in a giallo.
Plus, you get to see what a (presumably) cow's eye looks like when it's cut open. And, as a bonus, you can see what it would look like if a cardboard cut-out of a man was thrown from the top of the Eiffel Tower. And if that doesn't make you want to rush out and buy the film, then don't rush out and buy the film.
*Vernon did his own dubbing in the English version, and clearly relished the part. However, this is one of those occasions where if the director had sat in on the dubbing session, he may have demanded a different, more subtle performance.