While working on the post-production of the budget slasher flick Co-ed Frenzy, sound technician Jack Terry is given the task by his producer Sam to enhance the film's audio with a more authentic scream and improved wind sounds. During a recording session at a local park, Jack witnesses a tragic event when a car veers off the road and crashes into a creek. Although the male driver loses his life, Jack heroically saves a young woman named Sally Bedina and takes her to the hospital. While there, he is questioned by a detective about the accident, and in a twist of fate, he asks Sally for a drink. It comes to light that the car was being driven by Governor George McRyan, who is also a contender for the presidency, and Sally was his escort. An associate of McRyan, Lawrence Henry, persuades Jack to help keep Sally's involvement under wraps by aiding her escape from the hospital.
As Jack reviews the audio recording he made during the accident, he becomes alarmed when he hears what he believes to be a gunshot right before the tire blows out, leading him to suspect the incident was not accidental but rather an assassination. A news report reveals that a man named Manny Karp had captured the accident on film. When Karp sells photos from his footage to a local tabloid, Jack ingeniously combines those stills with his audio to create a rough film, where he notices a flash and smoke that suggest a gun was fired. Initially hesitant, Sally eventually agrees to participate in Jack's clandestine investigation of the accident. During their time together, Jack shares the harrowing story of how he left his previous role on a government commission to tackle police corruption after a wiretap operation led to the death of an undercover officer, Freddie Corso.
Unbeknownst to Jack, both Sally and Karp are part of a larger scheme involving McRyan. A rival candidate has enlisted a notorious thug named Burke to ensnare McRyan with Sally, who is posing as a prostitute. The plan involves taking scandalous photographs to coerce McRyan into withdrawing from the race. To further sabotage him, Burke decides to shoot out the tire of McRyan's vehicle, causing the deadly accident. Following a series of lethal cover-ups, including the murder of an innocent look-alike woman, Burke fabricates a fictional serial killer, "the Liberty Bell Strangler," to divert suspicion from himself.
In an effort to aid Jack's investigation into the circumstances surrounding McRyan's death, Sally undertakes the risk of stealing Karp's film, which, when aligned with Jack's audio, conclusively captures the gunshot that preceded the tragic blow-out. However, Jack finds that no one believes his account, and a far-reaching conspiracy quickly stifles his attempts to expose the truth. Local talk-show host Frank Donahue expresses interest in interviewing Jack and unveiling his tapes. Eventually, Jack consents, but Burke, keeping a close eye on their moves, masquerades as Donahue and urges Sally to meet him with the tapes.
As the situation escalates, Jack tracks Sally from a distance. His heart races when he realizes that her alleged ally is, in fact, Burke. Desperate to save her, Jack shoots off in pursuit, resulting in a harrowing crash into a department store window that leaves him incapacitated. Upon awakening in an ambulance, he discovers that Burke has managed to steal the incriminating film and disposed of it in a river. Listening through his earpiece, Jack witnesses the horrifying scene as Burke attacks Sally on a rooftop. Spurred into action, Jack confronts Burke, leading to a deadly struggle where he stabs him, only to tragically find that Sally has already been killed, leaving him shattered as he holds her lifeless body.
With Burke's demise and the evidence lost, Jack's audiotapes are ultimately insufficient to prove any wrongdoing, ensuring the conspiracy remains unexposed. In his grief and obsession, Jack repeatedly plays the recording of Sally's voice, becoming fixated on her death scream. Eventually, he incorporates this tragic scream into Co-ed Frenzy. Overjoyed at having found the perfect audio moment, Sam plays back the recording, forcing Jack to cover his ears against the haunting echoes of his past.
