400 years into the future, disease has wiped out the majority of the world's population, except one walled city, Bregna, ruled by a congress of scientists. When Æon Flux, the top operative in the underground 'Monican' rebellion, is sent on a mission to kill a government leader, she uncovers a world of secrets.

Gilda Bessé shares her Paris apartment with an Irish schoolteacher, Guy Malyon, and Mia, a refugee from Spain. As the world drifts toward war, Gilda defiantly pursues her hedonistic lifestyle and her burgeoning career as a photographer. But Guy and Mia feel impelled to join the fight against fascism, and the three friends are separated.