Steve Harmon, a Black sixteen-year-old, sits in his jail cell and writes in his notebook. Steve is about to stand trial for felony homicide. He decides to make a movie about his experience. Steve calls the movie Monster because that is what the prosecutor has called him. He tells his story through handwritten notes and a typewritten screenplay.

Steve’s lawyer, Kathy O’Brien, urges Steve to take his situation seriously because this crime could put him in jail for twenty years or more. Not only that, but Sandra Petrocelli, the State prosecutor, is a very good lawyer. Another problem for Steve is that James King, a young Black hood, is Steve’s co-defendant. James King has his own lawyer, Asa Briggs. Petrocelli, O’Brien, and Briggs make opening statements on the first day of Steve’s trial.

Petrocelli presents the charges against the defendants. She tells the jury that James King and Steve Harmon, along with two other criminals, robbed a drugstore. During the robbery, Aguinaldo Nesbitt, the fifty-five-year-old owner of the store, was killed. Petrocelli refers to the defendants as “monsters in the community.” She then calls two witnesses. José Delgado, an employee of the drugstore, tells how he found Mr. Nesbitt’s body and noticed that cash and cigarettes were missing. Salvatore Zinzi, a prisoner at the Riker’s Island jail, testifies that another prisoner, Wendell Bolden, told him about the drugstore robbery. Bolden testifies that he bought cigarettes from Bobo Evans and that Evans told him about the robbery. The two defense counsels, O’Brien and Briggs, establish that the witnesses are testifying for the State in return for reduced sentences. Flashbacks in Steve’s screenplay show Steve playing on the streets, listening to Mr. Sawicki, his film club mentor, and hanging out with James King and Osvaldo Cruz.

O’Brien tells Steve that her job is to make him a human being in the eyes of the jury. She explains that some jurors have decided against him just because he is young and Black, so Steve has to make the jury see him as different from the other defendants. Steve records suicidal thoughts and violent prison incidents. He compares himself with the other prisoners. Steve writes about his fear, anger, and pain and his rising sense of panic about the outcome of his trial. He also makes notes about his movie and about details he observes in court.

Petrocelli, the State prosecutor, calls more witnesses to establish the facts of the crime. The medical examiner states the time of Mr. Nesbitt’s death. Detectives Karyl and Williams describe their arrival at the crime scene. Asa Briggs, King’s attorney, establishes that the police have no fingerprint evidence. Petrocelli also calls an eyewitness, Mrs. Lorelle Henry, to the stand. Mrs. Henry testifies to being in the drugstore and seeing two young Black men arguing with the store owner. She identifies James King as being one of the two young men. Briggs establishes that the police had shown photos of King to Mrs. Henry before she picked him out of a lineup. The strongest witness for the State is Richard “Bobo” Evans, who admits that he took part in the robbery. Evans states that King was his partner in the robbery and that Steve served as the lookout.

The State rests its case. Briggs presents his defense of King. Dorothy Moore, a cousin of King’s, testifies that King was with her at the time of the robbery. Another witness testifies that King is left-handed. (The medical examiner’s evidence suggests that the shooter was probably right-handed.) Then it is O’Brien’s turn to present the defense of Steve. O’Brien tells Steve he will have to testify on his own behalf and put some distance between himself and King. She coaches Steve on how to answer questions on the witness stand.

Steve testifies that he did not take part in the drugstore robbery or discuss it with anyone before it happened. He states that he knows James King and Osvaldo Cruz, but only casually. Steve also states that he was not at the drugstore on the day of the crime but was walking around thinking about his movie. After Steve testifies, O’Brien puts Mr. Sawicki, his film teacher, on the stand. Sawicki states that he believes in Steve’s honesty as a filmmaker and as a person. The defense rests after Sawicki’s testimony.

Briggs makes the first closing argument in the case. He reminds the jury of the witnesses’ criminal records and contends that their unreliability casts reasonable doubt on King’s guilt. O’Brien follows and reminds the jury that the State has not proved any of its charges against Steve. She asks the jury to recall how Steve conducted himself on the witness stand and to compare Steve with Sal Zinzi, Bobo Evans, and Osvaldo Cruz before they decide who is believable. O’Brien reminds jurors of reasonable doubt and states firmly that Steve’s guilt has not been proven. In her closing argument for the State, Petrocelli stresses the importance of the stolen cigarettes in proving who committed the crime. She continues to assert that Steve served as the lookout for the robbery and is as guilty as the others.

The jury returns verdicts of guilty for James King and not guilty for Steve Harmon. After Steve hears the verdict, he turns to O’Brien for a hug. O’Brien gathers her papers and moves away, leaving Steve standing with outstretched arms. The image freezes as the screenplay ends.

Five months later, Steve is again writing in his notebook. He is at home with his parents and his brother Jerry. Steve spends his time making movies about himself, often with Jerry’s help. Steve’s parents are glad he is home, but the distance between Steve and his father is growing. Steve worries about why O’Brien turned away from him after winning the case. He wonders what O’Brien saw.