Polish-born mathematician Stan Ulam emigrates to the United States, where he joins the Manhattan Project and grapples with the moral weight of helping to develop nuclear weapons. As he navigates life as an outsider in a new country, he also tends to his ailing friend and colleague John von Neumann. The film balances personal drama with intellectual history, exploring how Ulam's work on thermonuclear weapons and his development of the Monte Carlo method shaped modern science.