Roberto, a drummer in a rock band, keeps receiving weird phone calls and being followed by a mysterious man.
Four Flies on Grey Velvet is a 1971 giallo film written and directed by Dario Argento.
Roberto tracks him to a deserted theatre and finds the stranger has produced a knife but is killed in the struggle. All the while a third person is taking photographs of the event from a gallery. Robert finds himself blackmailed but the blackmailer is not interested in money. The film was an Italian and French production between the Rome-based company Seda Spettacoli and the Paris based Universal. [wikipedia]