Gotham City, 1981. Arthur Fleck is an unlucky clown with mental problems who lives with his sick mother, a woman who worked for the millionaire Thomas Wayne. Arthur loses his job, the city is full of conflicts, his mother worsens his health. In that context, Fleck kills three young people on Wall Street who thought that, with his uncontrolled laughter, he was mocking them. It is the beginning of a criminal career driven by madness and social unrest.