In 1914, when World War I starts, her daughter Irene convinces her to run an X-ray unit on the Western Front in order to determine whether or not amputation is needed for wounded soldiers. Irene begins dating Frédéric Joliot, and Marie initially disapproves of that relationship because of their joint research into induced radioactivity, later asking Irene not to take part in Frédéric's future work on radioactivity because of possible effects on her health. Although Irene doesn't obey her mother, they go to the Western Front together to run the X-ray machine.