Brian De Palma’s best movie, Blow Out, opens with scene from a movie-within-a-movie, a Z-grade slasher rip-off called Co-ed Frenzy, from the director of such esteemed films as Blood Bath and Blood Bath 2, Bad Day at Blood Beach and Bordello of Blood. The camerawork mimics the killer POV shots of Black Christmas and Halloween, peeping through the windows of a sex-crazed sorority house before ducking inside, where the action alternates between T&A and stabbings. It finally ends with the umpteenth crude variation on the shower scene in Psycho, and the punchline that takes us out of the movie: the actor has a terrible scream.

Blow Out is about the sound man, Jack Terry (John Travolta), finding a better scream. It’s also about the movies, and about how easily the truth can be manipulated or obscured. Beyond that, it’s about what America had become after a decade where trust in the government was lost to Vietnam and Watergate, and how conspiracies of the powerful could crush ordinary citizens who happened to get in the way. Here was De Palma at the peak of his talent, making a film that’s politically loaded and emotionally operatic, with great technique, visual wit and an arsenal of sly references to other films and historical events. It’s so multi-layered, yet De Palma can make it feel like a magician’s sleight-of-hand.

Look again at that opening sequence. By that point in his career, De Palma could have people convinced that it wasn’t a movie-within-a-movie at all, but another lurid sequence from a director whose Hitchcockian thrillers were full of voyeurism and high-toned exploitation. After all, De Palma had already opened a film with a tracking shot through a girls locker room in Carrie and he had already done a softcore homage to Psycho in Dressed to Kill, which had Angie Dickinson lathering up while we anticipate her early exit. De Palma pulling out of the fake movie with that awful scream is not only a terrific joke, but a primer for the deconstructive trickery of the rest of the film. We’ll need to question everything we see and hear.

Despite garnering some of the best reviews of De Palma’s career, Blow Out tanked when it came out 40 years ago, most likely because audiences found the ending too despairing. Who could guess that juxtaposing the bicentennial celebration with a murder and a cover-up wouldn’t be commercially sound? But the film has lost none of its power over the years, as we’ve sunk deeper and deeper into media manipulation, conspiratorial thinking and a greater opacity among the governing elite and their ultra-wealthy patrons. What is, say, Jeffrey Epstein’s prison suicide but a Brian De Palma film waiting to happen?

True to form, De Palma used the films of the past as the building blocks to construct Blow Out, most directly Blow-Up, the 1966 Michelangelo Antonioni thriller about a fashion photographer who believes he’s captured a murder on a shoot, and Francis Ford Coppola’s The Conversation, itself a play on Blow-Up, only about a surveillance expert who believes he’s captured a murderous political conspiracy on tape. What De Palma did in conceiving his film was simple math: Blow-Up + The Conversation = Blow Out. Or, put another way, Image + Sound = Film.

The sound part comes first. The director of Co-ed Frenzy sends Jack out to get fresh sound effects, so he heads to a Philadelphia park at night with his microphone wand to get some authentic wind noises and the like. He happens to have the recorder on when a Chappaquiddick-like incident happens off in the distance, with a car careening off a bridge and into the creek water below. Jack rescues the young woman inside, Sally (Nancy Allen), and accompanies her to the hospital, where he learns that the driver of the car is a popular governor who could be the next president. One of the governor’s handlers takes him aside: would he mind, for the sake of the deceased’s wife and family, keeping his mouth shut about Sally being in the car?

The image part comes next. By a crazy coincidence, a sleazy photographer (Dennis Frantz) was also in the park and caught the incident on film, which he then sold to a tabloid, which prints the footage frame by frame. Only it’s not a coincidence: the photographer and Sally have been shaking down wealthy two-timers by putting them in a compromising position and asking for cash in exchange for the shots. Meanwhile, Jack makes something like a full-sound Zapruder film by syncing his recording with the printed frames, confirming his suspicion that the car’s tire was shot out before it veered off the bridge. He and Sally now possess knowledge too dangerous for them to have.

From there, Blow Out takes the basic form of the classic 70s political thriller, like The Parallax View or Three Days of the Condor, but De Palma gives the film a florid grandeur that’s far removed from the chilly paranoia of those earlier films. Travolta and Allen are fully invested in characters who develop a romantic bond under duress, and so when the stakes get high and the danger mounts, De Palma’s signature set pieces have a genuine emotional flavor on top of the amplified suspense. The ending seems particularly harsh because we’re so invested in Jack and Sally’s survival, along with the faint hope that justice against the powerful is possible to achieve in America.

Jack gets his scream in the end, but it’s a final, bitter irony that only he knows its source. The sound and images that Jack had once put together to reveal the shocking truth about a supposed accident are now gone, and the most horrific moment of his life is now ADR for a fictional piece of garbage. As a movie about making movies, Blow Out not only pulls the curtain back on how film-making works, but challenges the audience to question the reality of a medium that’s based around an optical illusion. Believe it or not, there are image-makers out there more sinister than Brian De Palma.