Carlos Smith is a Toronto defense attorney. He loves the fame that comes with winning high-profile clients on legal technicalities. He meets Andrea Dave, a former lover and prosecutor, who rejects his advances. Meanwhile, Archbishop Paul, a beloved figure and head of the Catholic Diocese of Toronto, is ambushed and killed by Andrew Shaw, a 19-year-old altar boy from Hamilton, who is arrested by the police. Carlos visits Andrew in prison and offers him a free will. Andrew reveals that he admired the archbishop. Carlos believes Andy to be innocent, meek and with a severe stutter. Andrea is assigned to prosecute him for first degree murder.
As the trial begins, Carlos learns that powerful civic leaders, including the corrupt Crown Attorney, John Arlott, recently lost millions in real estate investments due to Paul's decision not to develop church-owned land. . Following a tip from a former altar boy, Alex, about a videotape involving Andrew, Carlos steals a VHS cassette from the crime scene. The tapes show the archbishop forcing Andrew, his girlfriend Victoria and another altar boy to engage in sexual acts. When Carlos accuses Andrew of lying, he breaks down crying and uses his short name, Andy, a violent psychopath without stuttering. He accepts the archbishop's death and becomes physically violent. He becomes passive and shy and has no memory of the personality change.
Molly Jackson, the neuropsychologist examining Andrew, is convinced that he has dissociative identity disorder due to years of physical and sexual abuse at the hands of his father and Paul. Carlos is troubled by this information, as he cannot plead insanity in the ongoing trial. He decides whether or not to introduce evidence that will gain sympathy from the jury for Andrew, but may provide motive that Andrea cannot establish. She has the videotape anonymously given to the prosecution, knowing that she will realize who sent it, as she is under intense pressure to deliver a guilty verdict and will use the tape as evidence of motive.
At the trial, Carlos calls Andrew as a witness and questions him about the sexual abuse he suffered at the hands of Paul. He produces evidence that Andrea covered it up and that Paul molested another man. During Andrea's cross-examination and harsh interrogation, Andrew threatens to kill her, but is subdued and returned to prison. The judge informs Carlos and Andrea that she intends to dismiss the jury in favor of a bench trial, and will declare Andrew not guilty by reason of insanity, sending him to a psychiatric hospital.
Andrea is fired for losing the case and allowing Paul's crimes to be publicly exposed, but it is implied that she will resume her relationship with Carlos.
Carlos visits Andrew in prison to inform him of the dismissal. Andrew claims to have no memory of his violent reaction in the courtroom, but after Carlos leaves, he slips into asking about Andrea. When Carlos confronts Andrew, he reveals that he feigned a personality disorder. No longer stuttering, he boasts about killing Paul and Victoria. When Carlos asks her if there ever was an Andy, she replies "There never was an Andrew." Stunned and disillusioned, Carlos leaves the courthouse as Andrew/Andy taunts him from his cell.