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.
| Directing | Dario Argento | Director |
| Writing | Dario Argento | Screenplay |
| Writing | Dario Argento | Story |
| Writing | Luigi Cozzi | Story |
| Writing | Mario Foglietti | Story |
| Production | Salvatore Argento | Producer |
| Camera | Franco Di Giacomo | Director of Photography |
| Sound | Ennio Morricone | Original Music Composer |
| Editing | Françoise Bonnot | Editor |
| Art | Enrico Sabbatini | Production Design |
| Costume & Make-Up | Paolo Borselli | Hairstylist |
| Costume & Make-Up | Giuliano Laurenti | Makeup Artist |
| Crew | Carlo Rambaldi | Special Effects |
| Costume & Make-Up | Giovanni Morosi | Assistant Makeup Artist |
| Production | Angelo Iacono | Production Manager |
| Production | Roberta Leoni | Production Secretary |
| Directing | Roberto Pariante | Assistant Director |
| Art | Giuseppe Ciccocioppo | Props |
| Art | Mario Grilli | Decorator |
| Art | Franco Pedacchia | Set Dresser |
| Art | Giovanni Viti | Assistant Art Director |
| Sound | Massimo Anzellotti | Sound Effects Editor |
| Sound | Franco Bassi | Sound Mixer |
| Sound | Eugenio Fiori | Boom Operator |
| Sound | Mario Ronchetti | Sound Engineer |
| Crew | Dino Galiano | Special Effects |
| Camera | Mario Boccanegra | Grip |
| Camera | Roberto Carnevali | Still Photographer |
| Camera | Gastone Coppa | Key Grip |
| Camera | Umberto Dessena | Grip |
| Camera | Roberto Forges Davanzati | Assistant Camera |
| Lighting | Valerio Garzia | Gaffer |
| Lighting | Franco Gubiotti | Electrician |
| Camera | Giuseppe Lanci | Camera Operator |
| Lighting | Ennio Mancini | Electrician |
| Camera | Mauro Marchetti | Assistant Camera |
| Camera | Fernando Monti | Grip |
| Lighting | Anteo Pacini | Electrician |
| Lighting | Orazio Sinacore | Electrician |
| Camera | Gianfranco Transunto | Assistant Camera |
| Costume & Make-Up | Massimo Lentini | Assistant Costume Designer |
| Costume & Make-Up | Mina Manes | Tailor |
| Costume & Make-Up | Giovanni Viti | Wardrobe Assistant |
| Editing | Bruno Bianchini | Assistant Editor |
| Editing | Sergio Fraticelli | Assistant Editor |
| Sound | Bruno Nicolai | Conductor |
| Sound | Edda Dell'Orso | Musician |
| Directing | Patrizia Zulini | Script Supervisor |
| Production | Carlo Cucchi | Production Secretary |
| Production | Carlo Du Bois | Administration |
| Sound | Luciano Anzellotti | Sound Effects |
| Production | Giuseppe Mangogna | Unit Manager |
