Garson portrays the young Polish physics student Marie, who soon falls in love with and marries Dr. Pierre Curie (Walter Pidgeon), in whose lab she had worked. On their honeymoon they decide to investigate a strange effect Professor Becquerel (Reginald Owen) has noticed with the uranium/thorium stones for Marie's dissertation, and they determine there must be additional radioactive elements causing it. After years of experimentation in a makeshift lab at the University, they are finally able to isolate a few grains of a new element, radium, from 7 tons of raw material. Unfortunately, at the height of their success, tragedy strikes.