On May 7, 1945, just one day before the surrender of Nazi Germany to the Allies, Reichsmarshall Hermann Göring, portrayed by Russell Crowe, along with his family, voluntarily surrenders to U.S. forces stationed in Austria. This significant event reaches Associate Justice Robert H. Jackson, played by Michael Shannon, who is informed of Göring's capture during a crucial discussion with his secretary, Elsie, expertly depicted by Wrenn Schmidt. They engage in a debate regarding the establishment of an international tribunal aimed at charging the surviving leaders of the Nazi regime with their multitude of war crimes. While Elsie expresses her concerns about the lack of legal precedents for such actions, Jackson remains optimistic, seeing this tribunal as a rare chance to inaugurate a new legal framework.
Initially, the U.S. government shows hesitance towards Jackson’s proposal, favoring rapid executions instead. Nevertheless, Jackson's determination shines through as he secures the backing of Pope Pius XII by subtly hinting at his understanding of the Pope's controversial associations with the Nazis. Meanwhile, U.S. Army psychiatrist Lt. Col. Douglas Kelley, portrayed by Rami Malek, is called upon to assess the mental health of 22 prominent Nazi leaders, including Göring, who are in Allied custody and facing prosecution.
Kelley begins his evaluation at Bad Mondorf, Luxembourg, assisted by interpreter Sgt. Howie Triest (Leo Woodall). His early interactions with Göring appear cordial, although other prisoners like Robert Ley and Julius Streicher express contempt towards him. Kelley finds Göring to be intelligent yet deeply narcissistic, sparking his ambition to pen a tell-all book based on his observations.
As plans progress, Jackson and British lawyer Sir David Maxwell Fyfe (Richard E. Grant) are appointed as prosecuting counsels for the newly formed International Military Tribunal in Nuremberg, Germany. This tribunal seeks to address a range of serious charges including crimes against peace, war crimes, and crimes against humanity. As the trial approaches, Kelley and Göring's relationship evolves, with Göring helping Kelley communicate with his wife Emmy (Lotte Verbeek) and daughter Edda. Kelley's rapport with the Göring family intensifies, as he serves as a conduit for their messages, while also receiving requests from Jackson to keep him informed about the prisoners' legal defenses.
Tragedy strikes when Ley commits suicide in his cell, prompting Col. Burton Andrus (John Slattery) to call upon psychologist Dr. Gustav Gilbert (Colin Hanks) for a second opinion. The trial begins with Jackson delivering a powerful opening statement that emphasizes the urgent need for accountability. Göring, alongside his fellow detainees, pleads not guilty, despite the mounting evidence being presented against them. As the proceedings unfold, Kelley discovers that Göring's family has been arrested due to his involvement in art thefts, leading him to request intervention from Andrus.
During the trial, harrowing footage of the atrocities committed by the Nazi regime is shown, deeply unsettling Kelley as he confronts Göring, who continues to claim ignorance about these horrific events. Göring displays a defensiveness concerning the regime's actions, leading Kelley to despair and subsequently drown his sorrows in alcohol. In a drunken stupor, he inadvertently discloses sensitive discussions with Göring to a journalist from The Boston Globe, Lila (Lydia Peckham), resulting in dire consequences as Andrus relieves Kelley of his duties, despite having successfully negotiated the release of Emmy and Edda.
The narrative further unfolds as Triest confides in Kelley about his Jewish heritage and the tragic fate of his family during the Holocaust, warning of the complacency that allowed such atrocities to persist. As Kelley decides to surrender his notes to Jackson and Fyfe, he anticipates Göring's attempts to utilize the trial as a platform for a defense of the regime’s actions.
Göring's evasiveness in response to Jackson's cross-examination eventually leads to his brazen admission of loyalty to Hitler, a miscalculation that allows Fyfe to corner him effectively. Consequently, Göring is sentenced to death by hanging. In their final meeting, Kelley comes to terms with the darkness embodied by Göring.
As the gripping events unfold, on the night before his scheduled execution, Göring takes his own life by ingesting cyanide, eliciting anger from Andrus. Meanwhile, the remaining executions occur, marked by a distressing incident involving Streicher, who struggles at the gallows. Triest, aiming to confront Streicher with his identity, instead chooses to provide comfort.
Returning to the U.S., Kelley, haunted by his experiences in Nuremberg, publishes a work titled 22 Cells in Nuremberg, but finds it challenging to find an audience. The narrative encapsulates the aftermath of this impactful trial, illustrating Kelley’s descent into alcoholism and his attempts to warn against the potential resurgence of such regimes. In a tragic turn, Kelley ultimately takes his life in 1958. The film concludes with a poignant acknowledgment of Jackson’s efforts, which provide a crucial legal foundation for prosecuting war crimes internationally.