On December 23, 1991, Cameron Todd Willingham wakes to a house ablaze and, despite his frantic efforts, cannot save his three daughters. The tragedy becomes a public case as the prosecution frames the fire as deliberate arson, pointing to gasoline spread in a pentagram shape and a refrigerator moved to block the kitchen door. At the trial, witnesses portray a violent man, and a former cellmate, Johnny Webb, testifies that Willingham claimed the fire had been set on purpose. Despite Willingham and his wife Stacy insisting on his innocence, he is sentenced to death.
On death row, Willingham endures brutality from inmates and guards, and is placed in solitary for safety. The isolation takes a toll, and he experiences intense flashbacks to his life with Stacy while maintaining his protest of innocence. The relationship between Willingham and Stacy is complicated: she cheated on him, and he reacted with violence, yet they still care deeply for each other. Stacy’s communication with him wanes after her grandmother urges she stop replying, convinced of his guilt.
Seeking to prove his innocence, Willingham contacts a new lawyer, Reaves. He adapts to prison life by submitting to the harsh guards and befriending death-row inmate Ponchai James, with whom he expands his vocabulary and writing. James is eventually executed, leaving Willingham more determined to have his case reconsidered. A pivotal letter from Willingham to Reaves reaches Elizabeth Gilbert, a playwright who is moved by his plight. Laura Dern embodies Gilbert, whose ailing ex-husband and their two children insist that he is guilty, shaping the emotional landscape of Gilbert’s visit to the prison. There, she is struck by Willingham’s calm demeanor, and the two connect over their shared struggles as parents and their love for their children.
Willingham continues to immerse himself in art and poetry, and his bond with the guard Daniels grows; the guard begins to question Willingham’s guilt after watching him hallucinate about his daughters and reading his letters to Gilbert. Gilbert questions the witness statements and Reaves, who has made little progress in years, and travels to speak with Webb. When she interrogates Webb about allegations that the prosecutor paid him to lie about Willingham’s confession, he becomes agitated and threatens her.
As Willingham’s execution date approaches, new witnesses recant, but the defense’s efforts falter. The state’s case seems unshakable until Gilbert and Reaves confront Dr. Hurst, who reveals that the refrigerator had not been moved and that the fire could not have been arson as the jury was led to believe. Nevertheless, Reaves struggles to argue an appeal, and Hurst’s report is disregarded. Webb recants his testimony, yet Jackson keeps the case sealed in his favor. Stacy is pressured into testifying that Willingham confessed.
A cruel turn arrives when Gilbert suffers a car crash while Willingham is en route to execution, leaving her unable to witness a final moment. Willingham delivers a poignant speech from the death chamber, describing the growth he has achieved on death row and asking that his ashes be spread over his daughters’ graves. He dies under the supervision of guard Daniels, with Stacy and Reaves present as witnesses, and Gilbert, now paralyzed from the crash, later spreads his ashes with her own children nearby. The film closes with news footage in which Texas Governor Rick Perry denies guilt about ordering executions, leaving the question of responsibility unresolved in the public memory.
