In her final days, Marie Curie asks her daughter Irène to bury her with a small pouch. As Irène wonders about its meaning, Marie remembers arriving in France and meeting Anne Kowalski, a young Polish worker who gave her the pouch filled with soil from their homeland.

At the Sorbonne, Marie faces discrimination because she is Polish and a woman but begins working with Pierre Curie. Supported by industrialist Ruben Dupont, they isolate two new elements: polonium, named for Poland, and radium. Marie refuses to patent the discoveries, believing that scientific knowledge should belong to everyone. She and Pierre later receive the Nobel Prize in Physics.

Through Marie’s recommendation, Anne finds work at Dupont’s clock factory, where workers paint luminous dials with radium. As the substance is also promoted for consumer products and experimental cancer treatment, factory workers begin falling ill and dying. Dupont conceals the danger, attributing their deaths to other causes.

Pierre notices that radium damages the body and begins investigating Dupont’s hospital. Before he can expose the truth, he dies in a carriage accident. Marie concludes that radiation had weakened his bones and prevented him from avoiding the carriage.

Realizing that radium has harmed both Pierre and the factory workers, Marie demands that Dupont close the factory and stop the clinical trials. He agrees publicly but secretly continues production. Anne, devastated by the workers’ deaths and Marie’s hesitation to confront the truth, prepares to take her own life. Marie follows her and admits that although she did not initially understand the danger, she feared that revealing it would end her research. Anne accepts her apology.

Returning to her final days, Marie explains that the pouch contains the Polish soil Anne gave her. She confesses to Irène that her devotion to science often made her neglect her family and urges her daughter not to repeat her life. Irène assures her that, despite her regrets and mistakes, she lived a remarkable life.