Dwight Bradley Mason, an attorney highly respected for his devotion to the law, is visited by criminal lawyer Wayne Kellwin, an old schoolmate. Kellwin asks Brad to defend Rudi Wallchek, a young man accused of the robbery and knife-murder of Johnny Hulderman, the son of locksmith Peter Hulderman. Wayne explains that Brad's lack of trial experience might bring freshness to a seemingly hopeless defense for the impoverished Rudi. Brad declines, but after meeting District Attorney Joe Bucknor at a party and hearing his comments that Rudi will get the electric chair, Brad goes to see Rudi. Brad is impressed with the passive Rudi's admission to a life of crime and parting words that justice is not for people like him. Although Brad's lack of trial experience is evident, he wins the case by proving to the jury's satisfaction that Peter could not positively identify the killer because he was not wearing his glasses at the time. Brad is convinced that justice has been served until Peter confronts him and says that he has helped let a guilty man go free. Later, at Rudi's apartment, Brad realizes that Rudi's earlier demeanour had been an act and he is actually a slick hoodlum, who easily pays Brad $2,000 in cash for his defense. Some time later, Brad's loving wife Stella goes to Joe, who has come to respect Brad, to tell him that Brad is tortured by having unwittingly perverted the law. Meanwhile, Brad goes to see Peter and learns that Rudi actually killed Johnny over protection money. When a broken Peter asks Brad to defend him after he kills Rudi, Brad says that there must be another way and takes a reference key to Rudi's apartment that Peter kept after repairing the lock weeks before. Brad then goes to Joe, who has a hunch that there is a very powerful person at the top of the city's crime syndicate. Although Joe tells Brad that he has no evidence to prove Rudi's ties to the syndicate, he orders his men to follow Rudi. As Brad is leaving the building, he sees a body being brought into the morgue and overhears the ambulance driver say that the body was Peter, who was hit by a truck that morning. Brad then takes the key and sneaks into Rudi's apartment. While there, Brad answers the phone and hears a vaguely familiar voice order Rudi to meet him at 9:30 sharp. Before Brad leaves the apartment, he finds a walking stick concealing a thin knife like the one used in Johnny's murder, and wraps it in Rudi's laundry receipt, then leaves. Brad tries for hours to question local shopkeepers about the protection racket, but no one will talk. Frustrated, he goes to the penthouse of Andrew Jason Layford, a prominent friend who heads the crime commission. During their conversation, the bell rings and Andrew leaves the living room. While he is gone, Brad notices an electric blender mixing a milkshake and recognizes the strange buzzing sound as the one he heard on the phone in Rudi's apartment. He then looks at his watch and sees that it is 9:30. When Andrew returns, Brad carefully reveals what he suspects about Andrew being the head of the crime syndicate. Although Andrew does not admit to anything, he lets Brad know that things might happen to his family if the charges came out. Suddenly, Brad stabs Andrew in the heart with the thin knife. The next morning, a remorseful Brad tells everything to Stella and wants to confess, but she tells him that justice, if not the law, has been served and begs him not to destroy their family. That afternoon, Rudi is arrested for Andrew's murder because his fingerprints were found on the knife, and the police, who had been following Rudi, saw him enter Andrew's apartment building at 9:30. Brad is stunned that Rudi has been charged with the crime and decides to defend him, hoping that he will not be wrongly convicted. The evidence overwhelmingly points to Rudi as the killer, and Brad's only defense is the suggestion that someone else had been in Andrew's apartment. After Rudi is convicted, Brad's son Bob, who is about to graduate from law school, tries to console him, but Brad tells Bob that he will soon be taking over the practice. Brad then goes to Joe to confess, realizing that Joe had begun to suspect who the real killer was. Joe explains that although the crime rate has dropped significantly since Andrew's death, he still must bring the killer to justice, even if he is a friend. Brad asks for five minutes alone with Rudi and goes to his cell. There Brad tells Rudi that he killed Andrew, then shows him the thin knife he had secretly taken from Joe's desk. Seeing a bible in the cell, Brad goes to it, turning his back on Rudi, who stabs him to death just as Joe and the guards arrive. A short time later, Joe concludes the commencement address at Bob's graduation, urging the new lawyers to keep their hands clean, just as Brad did.