Prestonville State University Campus is being terrorized by a serial killer known as "Deathmask". This is due to the bizarre death mask he always leaves on his victims after strangling them, and he targets blond women. So far he has claimed five victims. Deathmask has prompted vigilante fervor, both among the town residents and the Main Student Alliance, who persist in patrolling the campus and escorting women, despite pleas from Mayor Tom Fowler to let the authorities handle Deathmask. Leading the Deathmask investigation is Chief Frank Rhodes, who does not approve of the self-defense classes that Joan Singer runs in the school for female students because of his chauvinistic attitudes. There has been aggravation between them for six months over it.
David is studying in the library, where he also works under the name of Brent. He escorts one student, Miriam (also a blonde) to the self-defense classes. Joan's classes are attracting press attention, and also controversy over whether such classes are appropriate or effective for women. Joan defends her classes, and underlines her point by flipping the reporter. Rhodes is watching and tries a different tactic by offering to make peace with Joan with an invitation for a drink. She declines as she already has a date with David.
Deathmask claims his sixth victim, Maggie Long. There is evidence Maggie fought back, using her self-defense tactics, before she was killed. This prompts further disapproval from Rhodes about Joan's self-defense classes and teaching women to resist attackers. Joan herself begins to doubt her classes, but David persuades her otherwise. He also learns that Joan herself was a near-victim of a killer, and only fighting back saved her.
Meanwhile, David is drawing suspicion from Rhodes, and also from Jenks, who leads the vigilante Main Student Alliance. Things come to a head in the library where David is helping Miriam. Jenks and his friends approach him with menace. Rhodes intervenes and offers to take David down to the station for a checkout to lift the suspicion from him. David asks if he can come the next day. Rhodes agrees, but orders his associate Sid to watch David.
Unfortunately, Sid has a habit of nodding off, which is precisely what he is doing by the time it is nightfall and David is escorting Miriam. David says he is leaving town and asks Miriam to give a note to Joan. Miriam hops into her car while David goes off on his own. But Miriam does not realize Deathmask is in the car and he starts grabbing her from behind. David realizes what is happening and jumps on the car while Deathmask drives wildly, trying to shake him off. Deathmask succeeds in shaking off David, but then the car gets stuck between two others. Miriam jumps out and tries to run, but Deathmask is onto her.
But David hulks out and soon the Hulk is onto Deathmask. He scares Deathmask off, but Deathmask gets away while the police arrive and see the Hulk. The Hulk takes off while the police and Jenks find the hysterical Miriam, who keeps moaning "David". They jump to the wrong conclusion over this and David is arrested on suspicion of being Deathmask.
As David is led to the police station/courthouse building, he is accosted from all sides from the townsfolk, who are in an ugly mood. J.J. Hendren, whose daughter Peggy was a Deathmask victim, is the leader of the pack. Rhodes is worried that the courthouse has insufficient security against such potential lynch mob behavior and wants to move David to higher security. But Fowler is more interested in the political brownie points he will gain from the confession and conviction of Deathmask in his bid to become governor. Rhodes is disgusted at this.
Meanwhile, Joan believes David is innocent and goes live on TV about it. Deathmask sees this and intends to make her his next target (she is blond too). He is also having flashbacks that indicate he has been badly affected by his encounter with the Hulk.
Outside the courthouse, while Rhodes interrogates David, Fowler is milking all the political benefits he can get out of the Deathmask arrest he can get to the press. He brags to the press (among whom is McGee) that they have the killer and making promises that they will have the confession real soon. Sid comes out and confirms that Rhodes is indeed extracting a confession (which is a blatant lie). Joan protests against Fowler's conduct, as it violates the law and David's rights, and again claims that David is innocent. Fowler ignores her and she goes off in a huff.
The ugly townsfolk are still lurking outside the courthouse. Realizing that David will be moved to higher security soon, Hendren hatches a plan for them to storm the courthouse that night and lynch David. Jenks protests, but Hendren does not listen to him. Instead, he needles Jenks into joining the lynching.
Meanwhile, Rhodes interrogates David (alone and with no attorney allowed for David, despite his request for one). He has extracted no confession, but has discovered David has been using other aliases and, knowing all types of people and can empathize with them, realizes that David is a runner. But the interrogation starts taking strange turns, with Rhodes babbling about Janus, the two-headed god who is always chasing Rhodes. They also overhear Fowler's conduct outside and Rhodes expresses outrage at such "slimeball" politics. David begins to suspect that Rhodes knows he has the wrong man. But when David asks about what Miriam had to say about the attack (and can say he is not Deathmask), Rhodes says that Miriam is under sedation and unable to talk.
So far Rhodes has given the impression that he is an honest cop, but then his demeanor starts to change in bizarre ways as he talks about his father, who always went after "cheap blondes". He would take Rhodes along so his wife would not suspect while he did things to them. Sensing where things are heading, David quietly turns the microphone of the tape recorder that is recording the interrogation in the direction of Rhodes. As the conversation continues, it becomes apparent that Rhodes has a split personality: his honest cop side, and a dark side that has misogynistic tendencies towards blond women and despises Rhodes as a weakling. And when Rhodes exclaims, "Get back, get away from me!", David remembers that Deathmask spoke the same words, and in the same tone, back in the car. David now realizes Rhodes is Deathmask but plays it cool, trying to persuade Rhodes to seek help.
Meanwhile the lynch mob has assembled outside. They have cut telephone wires, and are armed and have their faces concealed. Rhodes sees them and starts commenting on them all wearing masks; he has a fascination for masks.
Rhodes now starts becoming really unstable. When David asks him if he is all right, he starts telling David (ironically) that he has no idea what it is like to have something horrible inside you, something that might burst out and has to be kept locked away.
Then the cassette runs out. Hearing the click, Rhodes realized that it had recorded what he was saying. He rips it up, cuffs David and then leaves, expressing his desire to go after Joan, and there is no choice about it: in his view, her self-defense tactics were to blame for Maggie's death. He walks out to deal with Joan, paying no heed to the mob around him or Fowler banging on the door, yelling there is a lynch mob outside.
The lynch mob's violence breaks loose, with McGee and Sid being the first victims of it. The mob then smash their way into the courthouse and the interrogation room, where they start attacking David. This triggers a hulk-out, which the mob cannot see because they are all piling on top of David. Once transformed, Hulk brushes off the assailants, smashes his way out of the courthouse, and goes after Rhodes. McGee is very surprised at the Hulk's appearance, while the attackers have been subdued by it. Their fate afterwards is not recorded.
Rhodes is in the process of attacking Joan when the Hulk comes bursting in on the scene. Rhodes climbs scaffolding to get away, but the Hulk rips it down. This knocks Rhodes to the ground, but he survives. The Hulk takes off.
Joan rips off Rhodes' mask, revealing who Deathmask really is to her and the now-arrived police. Rhodes talks to Joan while his split personality changes. First the Deathmask personality says Rhodes deserves to die and could never survive. Then the Rhodes personality takes over and says: "inside me Joan – it's him."
This time, the townsfolk are better behaved while they wait outside the courthouse to hear news of Deathmask. The ringleaders of the lynch mob are absent, which suggests they were arrested for it and are now in custody. Outside, Joan meets up with Miriam and it is revealed that Rhodes kept her sedated to prevent her from revealing what she knew about his attack. Rhodes comes out in handcuffs to a waiting police car, and the townsfolk stay restrained. Rhodes gives Joan one last dark look when he sees her. There is no sign of David (who is back to hitch-hiking). Joan assumes he quite understandably left town, never to return, because the treatment he received.