In 1945, the successful testing of the first atomic bomb marks a significant achievement for J. Robert Oppenheimer, who served as the director of the Manhattan Project at Los Alamos. However, as the political landscape shifts, key decisions regarding the bomb’s deployment are taken out of Oppenheimer’s hands and those of his fellow scientists. Following that momentous test, President Harry S. Truman orders the bombings of Hiroshima and Nagasaki, ignoring Oppenheimer’s insistence that Truman should inform Stalin before any action was taken against Japan. This oversight escalates tensions with the Soviets, leading Oppenheimer to believe that these events initiated the nuclear arms race.

Despite receiving public accolades, Oppenheimer struggles with profound guilt over the mass destruction and deaths caused by the bomb. His confrontation with Truman reveals this torment, as Oppenheimer admits his remorse, only to be reprimanded by Truman, who reinforces his own accountability for the decision to use the weapon. Oppenheimer argues for the limitation of nuclear armament development—a plea Truman dismisses, showing the chasm between them.

In the backdrop, Rear Admiral Lewis Strauss, a retired Naval officer and senior member of the U.S. Atomic Energy Commission (AEC), emerges as a key antagonist. Strauss, who had previously appointed Oppenheimer as a scientific advisor to the AEC after the war, finds Oppenheimer’s influence contentious. As Oppenheimer contends for control over nuclear proliferation, the AEC’s interest in Teller’s hydrogen bomb rises amid the escalating Cold War. Oppenheimer, aware of the significant technical challenges, discourages pursuing the hydrogen bomb, while advocating for international control over nuclear weapons.

Tensions escalate as AEC Chairman Lewis Strauss, deeply resentful after being publicly rebuffed by Oppenheimer regarding the export of radioisotopes—used by other nations to assist in developing atomic capabilities—feels humiliated. Oppenheimer’s suggestions for U.S.-Soviet negotiations post their own bomb detonation further alienate him from Strauss, who believes that if the U.S. develops a hydrogen bomb, the Soviets will have no choice but to follow suit.

With Oppenheimer’s opposition to the hydrogen bomb program, Truman ultimately approves its development, despite the scientist’s dire warnings. Strauss, convinced of Oppenheimer’s supposed collusion with the Russians during the Manhattan Project, plots to undermine Oppenheimer’s political standing. In a calculated move, he orchestrates a private hearing on Oppenheimer’s security clearances in 1954, leading to a verdict that appears predetermined.

The hearing is marked by manipulation and bias, particularly through the actions of Roger Robb, who is appointed as special counsel by Strauss. While Robb has comprehensive access to Oppenheimer’s security file, Oppenheimer’s legal representation is left in the dark. The outcome devastates Oppenheimer’s reputation, as the board rescinds his Q clearance, significantly diminishing his influence over nuclear policy.

In 1959, during Strauss’ Senate confirmation hearing for the Secretary of Commerce position, accusations arise about his motivations behind orchestrating Oppenheimer’s disgrace, ultimately leading to a Senate vote against his nomination. A gesture of redemption arrives in 1963 when President Lyndon B. Johnson awards Oppenheimer the Enrico Fermi Award, symbolizing a shift in his public perception. Flashbacks showcase a pivotal conversation between Oppenheimer and Einstein, revealing Oppenheimer’s lingering belief that their actions had unleashed a catastrophic chain reaction—the nuclear arms race—that could ultimately lead to global destruction.