After British Detective Sergeant “Johnny” Johnson severely beats a suspected pedophile at police headquarters, he reflects on events leading up to that attack: Following the rape of three young girls in a London suburb, Johnson and fellow police detectives keep watch at the local school, where children are met by anxious parents. Frustrated that their presence has frightened away the perpetrator, Johnson grows more incensed when a report comes in soon after that one of the schoolgirls who was not met by an adult has gone missing. Joining a police search at dusk, Johnson explores the underbrush alone where eventually he finds the missing girl, Janie Edmonds, with torn, muddy clothes. Hoping to get details from Janie, Johnson rides to the hospital with her, but learns nothing. Later, at police headquarters, Johnson insults a witness who earlier saw Janie meet a man in a long, dark coat but who waited to pass on the information until it was too late. Johnson then prowls the streets and questions a regular informant in vain. In the early morning, two policemen spot a man covered in mud, staggering about and unable to speak, and bring him to the station. Noting blood on his dark coat, and scratches on his face, Inspector Cameron and partner Frank Jessard believe the man may be the molester. Eager to question the man, Johnson joins Cameron and the suspect, who has identified himself as Kenneth Baxter. Although Baxter refuses to make a statement, Johnson agrees with the others on the suspect's guilt. When Cameron orders Baxter be let alone for a while to “sweat,” however, Johnson grows indignant, believing that Baxter is making a mockery of them by avoiding answering questions. Soon after, Johnson returns to the interrogation room where he orders the guard to leave so that he and Baxter are alone. While Johnson questions Baxter, Cameron meets with the chief constable, who scolds him for holding Baxter without charging him or allowing him contact with a solicitor. Back in the present, Cameron leads Johnson to another room where he files a report on his attack on Baxter. Afterward, the chief suspends Johnson and orders him to remain at home. On the drive back to his flat, Johnson reflects on the numerous gruesome results of violent acts that he has witnessed over his twenty years on the force. Upon arriving home, Johnson begins drinking, which wakens his wife Maureen, who grows unsettled by her husband’s mood but refrains from asking him its cause. Soon, the couple quarrels as Johnson wants to talk about the beating and the case, yet cannot find the appropriate words to make his wife understand his conflicted, angry emotions. Pleading with Johnson to confide in her, Maureen nevertheless is horrified when he describes the numerous brutal scenes he has dealt with over his career. Overcome with frustration, Johnson lashes out at his wife, blaming her plainness and physical unresponsiveness as the major failings of their marriage. As Johnson criticizes his wife, he recalls that when he found Janie lying in the forest, she struggled against him in terror. Declaring that he hopes Baxter dies because he is a pervert, Johnson is interrupted by the doorbell as Cameron and another detective arrive. Cameron informs Johnson that Baxter has died from the beating, requiring Johnson to return to headquarters immediately. After shaving and changing clothes, Johnson departs without a word to Maureen. At headquarters, Detective Superintendent Cartwright meets Johnson alone in an interrogation room. Initially Johnson responds sulkily to Cartwright’s request to describe all that occurred with Baxter, claiming that the details are in his report. Cartwright explains that he must find “something like the truth” in order to help Johnson and assures him whatever he says will be considered truthful. Johnson then haltingly explains his frustration with Cameron who allowed Baxter to mock them, by refusing to answer their questions, then repeats his certitude of Baxter’s guilt. During the daylong interrogation, Johnson grows increasingly distressed over his inability to convince Cartwright of Baxter’s guilt and his sense of rightness. At one point, Johnson, intent on demonstrating his strategy with Baxter, firmly takes Cartwright’s hands, accidentally burning Cartwright with his own cigarette. Although perturbed by Johnson’s clear emotional disturbance, Cartwright continues the interrogation. As the hours pass, Johnson attempts to describe the gruesome images of past crime scenes that plague him, but does not relate the additional haunting images of Janie lying in the forest smiling at him, or Baxter’s bloodied, grinning face during the beating. Finally Johnson bitterly suggests that Cartwright and other high-ranking detectives intentionally allow subordinates to take the blame in troublesome cases and have forgotten the grisly, daily life of police work. Incensed, Cartwright declares that Johnson is a bullying brute, stuck in his low rank by his inability to deal with his work in a professional manner, choosing instead to blame everyone else for his own weaknesses. Exhausted, Cartwright pronounces his disgust with Johnson, but vows to present his case to the best of his ability to the senior officers. After the superintendent’s departure, Johnson recalls the actual events of Baxter’s beating: Johnson begins his interrogation by asking Baxter about his day, then about his wife and two daughters and quickly maneuvers the suspect into admitting he rarely has sex with his wife. When Baxter refuses to acknowledge how he channels his sexual impulses, Johnson grabs his hand and squeezes it until it is nearly broken. As Baxter realizes that Johnson’s angry tirades are increasingly more about the policeman's personal failings and frustrations, he calls the detective a “sad, sorry little man,” which results in a savage blow from Johnson. Recovering, Baxter demands to see Johnson’s superior, but is refused. Accepting Johnson’s handkerchief to mop his bloody nose and mouth, Baxter confides that he has always hated bullies like Johnson, having learned early in school that a bully needs a victim, and so he has always felt superior to those who tried to bully him. After Baxter laughs at the detective’s attempt to suggest a psychological reason behind his character, Johnson beats him again. Although aching and bleeding, Baxter insists he went to the pictures the afternoon that Janie was attacked, then baits Johnson, pointing out that it takes a pervert to know one. Johnson furiously resumes the assault only to be brought up short when Baxter proclaims that nothing he has done is as bad as the images within Johnson’s mind. Sensing a victory over Johnson, Baxter scoffs that the detective does not know anything about himself and is paralyzed by the fear of acting on his dark thoughts. Taken aback, Johnson candidly asks Baxter if he suffers the same torment and wonders if Baxter can help him. Taking Baxter’s hand once more, Johnson pleads for help and when the revolted Baxter tells him to help himself, Johnson administers the fatal blows. Back in the interrogation room in the present, Johnson mutters that he had no choice in the assault, in which Baxter played the victim in order to help him.