After the success of the Manhattan Project, Los Alamos continued its groundbreaking nuclear research and experiments. On May 21, 1946, Louis Alexander Slotin, a brilliant but soon-to-be-retired scientist, conducts a criticality demonstration for his successor, surrounded by a room full of his peers.

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In this dangerous experiment, Slotin uses nothing more than a flathead screwdriver and his bare hands to manipulate a plutonium core — a procedure he had performed countless times before. But this time, a fatal miscalculation causes the core to reach a supercritical state. With the room now at risk of lethal radiation, Slotin acts quickly, moving to remove the reflective dome that is sustaining the dangerous reaction. But in doing so, he seals his own fate, knowing the radiation has already taken its toll. He has only nine days left to live.

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As Slotin struggles to survive the devastating effects of radiation poisoning — severe burns on his organs, gangrene, and limbs slowly dissolving — he reflects on the life he’s led — remembering the events leading up to and surrounding the incident. These include a visit from the woman he loves, Betty Wilson — who now stops at nothing to be

at his side.