The plot is one of those concoctions that makes the action barely possible. The hero, a barber-soldier in World War I, saves the life of a German pilot named Schultz and flies him to safety, all the time not even knowing he was the enemy. Their crash-landing gives the barber amnesia, and for 20 years he doesn't know who he is. Then he recovers and returns to his barber shop in the country of Tomania (say it aloud), only to discover that the dictator Hynkel has come to power, not under the swastika, but under the Double Cross. His storm troopers are moving through the ghetto, smashing windows and rounding up Jews (the term "concentration camp" is used early, matter-of-factly). But the barber's shop is spared by the intervention of Schultz, now an assistant minister, who recognizes him.

The barber (never named, just like the Tramp) is in love with the maid Hannah (Paulette Goddard, Chaplin's estranged wife at the time). And he is befriended by his former neighbors. But he and the disloyal Schultz are eventually put in a concentration camp, and then Hynkel has a boating mishap, is mistaken for the barber, and locked into the camp just as the barber and Schultz escape -- with Hynkel's uniform. Now the barber is assumed by everyone to be the dictator.

In the classic Chaplin tradition, the movie has a richness of gags and comic pantomime, including Hynkel's famous ballet with an inflated balloon that makes the globe his plaything. There is a sequence where five men bite into puddings after being told the one who finds a coin must give his life to assassinate Hynkel. None of them want to find the coin and there is cheating, but eventually -- see for yourself. And there is a long, funny episode when the dictator of neighboring Bacteria, Benzini Napaloni (Jack Oakie), pays a state visit. Napaloni, obviously modeled on Mussolini, eludes an attempt to make him sit in a low chair so the short Hynkel can loom over him. And when the two of them sit in adjacent barber chairs, they take turns pumping their chairs higher than the other. There is also a lot of confusion about saluting, and Chaplin intercuts shots of the two dictators with newsreels of enormous, cheering crowds.

In 1940, this would have played as very highly charged, because Chaplin was launching his comic persona against Hitler in an attempt, largely successful, to ridicule him as a clown. Audiences reacted strongly to the film's humor; it won five Oscar nominations, for picture, actor, supporting actor (Oakie), screenplay and music (Meredith Willson). But audiences at the time, and ever since, have felt that the film comes to a dead end when the barber, impersonating Hynkel, delivers a monologue of more than three minutes which represents Chaplin's own views.