Roberto, a drummer in a rock band, keeps receiving weird phone calls and being followed by a mysterious man. One night he manages to catch up with his persecutor and tries to get him to talk but in the ensuing struggle he accidentally stabs him. He runs away, but he understands his troubles have just begun when the following day he receives an envelope with photos of him killing the man. Someone is killing all his friends and trying to frame him for the murders.
You can now watch Four Flies on Grey Velvet online on the following streaming providers in the United States.
| Writing | Dario Argento | Screenplay |
| Writing | Dario Argento | Story |
| Directing | Dario Argento | Director |
| Writing | Mario Foglietti | Story |
| Writing | Luigi Cozzi | Story |
| Production | Salvatore Argento | Producer |
| Camera | Franco Di Giacomo | Director of Photography |
| Art | Enrico Sabbatini | Production Design |
| Editing | Françoise Bonnot | Editor |
| Sound | Ennio Morricone | Original Music Composer |
| Costume & Make-Up | Giuliano Laurenti | Makeup Artist |
| Costume & Make-Up | Paolo Borselli | Hairstylist |
| Crew | Carlo Rambaldi | Special Effects |
| Costume & Make-Up | Giovanni Morosi | Assistant Makeup Artist |
| Camera | Umberto Dessena | Grip |
| Production | Roberta Leoni | Production Secretary |
| Camera | Mario Boccanegra | Grip |
| Lighting | Orazio Sinacore | Electrician |
| Editing | Bruno Bianchini | Assistant Editor |
| Camera | Fernando Monti | Grip |
| Directing | Roberto Pariante | Assistant Director |
| Editing | Sergio Fraticelli | Assistant Editor |
| Production | Angelo Iacono | Production Manager |
| Art | Mario Grilli | Decorator |
| Art | Franco Pedacchia | Set Dresser |
| Directing | Patrizia Zulini | Script Supervisor |
| Art | Giovanni Viti | Assistant Art Director |
| Sound | Mario Ronchetti | Sound Engineer |
| Camera | Roberto Forges Davanzati | Assistant Camera |
| Lighting | Valerio Garzia | Gaffer |
| Sound | Edda Dell'Orso | Musician |
| Art | Giuseppe Ciccocioppo | Props |
| Camera | Gastone Coppa | Key Grip |
| Lighting | Ennio Mancini | Electrician |
| Sound | Franco Bassi | Sound Mixer |
| Crew | Dino Galiano | Special Effects |
| Camera | Mauro Marchetti | Assistant Camera |
| Sound | Bruno Nicolai | Conductor |
| Camera | Roberto Carnevali | Still Photographer |
| Lighting | Franco Gubiotti | Electrician |
| Costume & Make-Up | Massimo Lentini | Assistant Costume Designer |
| Costume & Make-Up | Mina Manes | Tailor |
| Production | Carlo Du Bois | Administration |
| Sound | Massimo Anzellotti | Sound Effects Editor |
| Camera | Giuseppe Lanci | Camera Operator |
| Lighting | Anteo Pacini | Electrician |
| Sound | Eugenio Fiori | Boom Operator |
| Camera | Gianfranco Transunto | Assistant Camera |
| Costume & Make-Up | Giovanni Viti | Wardrobe Assistant |
| Production | Carlo Cucchi | Production Secretary |
| Sound | Luciano Anzellotti | Sound Effects |
| Production | Giuseppe Mangogna | Unit Manager |
