Bankrupt comedian Arthur Fleck (Joaquin Phoenix) has long walked a fine line between reality and madness. One day, he wanders the streets of Gotham City in his clown suit and comes into conflict with brutal thieves. Slowly, a spiral of events reaches terrifying proportions. Abandoned by all, Fleck begins to sink further and further into the depths of madness, gradually transforming into the criminal icon the world will soon know as the Joker.