After World War II, tensions build between the Soviet Union and the U.S. Scientists at Los Alamos continue developing nuclear weapons, helped by the recently-reconfigured ENIAC. Using a statistical method called Monte Carlo, they optimize nuclear weapons through computer simulations. In these simulations, physics is neither purely experimental nor theoretical–it’s both, creating what historian Peter Galison calls a “netherland…at once nowhere and everywhere.” And Klári finds herself immersed in this sort of netherworld, turning nuclear physics into code.