This could have worked better for me had Dario Argento not cast the pretty hapless Michael Brandon in the lead. He is "Roberto", a drummer in a mediocre rock band who gets it into his head that he is being followed! One night, he lies in wait for and apprehends this man in a derelict opera house - but in the ensuing struggle he manages to stab his phantom and kill him. If that wasn't bad enough, the next day he receives some photographs of him doing that very deed and his is now, of course, ripe for blackmail. But by whom? Why? In any case he'd better find out pronto as gradually we discover that many associated with him are falling foul of his new nemesis too! At times this is actually quite (deliberately) funny. Perhaps a little contrived at times, but there are moments that raise a smile as the characters all trip over themselves to get in (and out) of the action. The ending - well that's a turn up for the books that really does make the film worth sticking with. Not Argento's best work, though quite possibly Brandon's, and though it's a bit too long and a bit thinly spread, it's still just about worth a gander.