Citizens and dignitaries are assembled for the unveiling of a new monument to "Peace and Prosperity". After droning speeches the veil is lifted to reveal the Little Tramp asleep in the lap of one of the sculpted figures. After several minutes of slapstick he manages to escape the assembly's wrath to perambulate the city. He rebukes two newsboys who taunt him for his shabbiness, and while coyly admiring a nude statue has a near-fatal encounter with a sidewalk elevator.
The Tramp encounters the beautiful flower girl on a street-corner and in the course of buying a flower realizes she is blind; he is instantly smitten. Through an aural coincidence the girl mistakes her customer for the wealthy owner of a chauffeured automobile.
That evening the Tramp saves a drunken millionaire from suicide. The millionaire takes his new best friend back to his mansion for champagne, then (after another abortive suicide attempt) out for a night on the town. After helping the millionaire home the next morning, he sees the flower girl en route to her street-corner. The Tramp gets some money from the millionaire and catches up to the girl; he buys all her flowers and drives her home in the millionaire's car.
After the Tramp leaves, the flower girl tells her grandmother (Florence Lee) about her kind and wealthy friend. Meanwhile, the Tramp returns to the mansion, where the millionaire – now sober – does not remember him and has him thrown out. Later that day, the millionaire is once more intoxicated and, seeing the Tramp on the street, invites him home for a lavish party. But the next morning history repeats itself: the millionaire is again sober and the Tramp is again out on his ear.
Finding that the girl is not at her usual street-corner, the Tramp goes to her apartment, where he overhears a doctor tell the grandmother that the girl is very ill: "She has a fever and needs careful attention." Determined to help, the Tramp takes a job as a street sweeper.
On his lunch break he brings the girl groceries while her grandmother is out selling flowers. To entertain her he reads a newspaper aloud; in it is a story about a Viennese doctor's blindness cure. "Wonderful, then I'll be able to see you," says the girl – and the Tramp is struck by what may happen should she gain her sight and discover that he is not the wealthy man she imagines. He also finds an eviction notice the girl's grandmother has hidden. As he leaves, he promises the girl that he will pay the rent.
The Tramp returns to work to find himself fired – he has been late once too often. A boxer convinces him to fight in a fake bout; they will "go easy" on each other and split the prize money. But the boxer flees on learning he is about to be arrested, and is replaced by a no-nonsense fighter who knocks the Tramp out despite the Tramp's creative and nimble efforts to keep out of reach.
The Tramp encounters the drunken millionaire a third time and is again invited to the mansion. The Tramp relates the girl's plight and the millionaire gives him money for her operation. Two burglars knock the millionaire out and flee with the rest of his money. The police find the Tramp with the money given him by the millionaire, who because of the knock on the head does not remember giving it. The Tramp evades the police long enough to get the money to the girl, telling her he will be going away for a time, but in due course he is apprehended and imprisoned.
Months later the Tramp is released. He goes to the girl's customary street corner but she is not there. We learn that the girl – her sight restored – now runs a busy flower shop with her grandmother. But she has not forgotten her mysterious benefactor, whom she imagines to be rich and handsome: when an elegant man enters the shop she wonders for a moment if "he" has returned.
The Tramp happens by the shop, where the girl is arranging flowers in the window. He stoops to retrieve a flower discarded in the gutter. After a brief skirmish with his old nemeses, the newsboys, he turns to the shop's window through which he suddenly sees the girl, who has been watching him without (of course) knowing who he is. At the sight of her he is frozen for a few seconds, then breaks into a broad smile. The girl is flattered and giggles to her employee: "I've made a conquest!" Via pantomime through the glass, she kindly offers him a fresh flower (to replace the crushed one he took from the gutter) as well as a coin.
Suddenly embarrassed, the Tramp starts to shuffle away, but the girl steps to the shop door and again offers the flower, which he shyly accepts. She takes his hand and presses the coin into it, but abruptly she stops; her smile turns to a look of puzzlement. She runs her fingers along his arm, his shoulder, his lapels, then catches her breath: "You?" The Tramp nods with an uncertain smile and asks, "You can see now?" The girl replies, "Yes, I can see now" and tearfully pulls his hand to her bosom. The uncertainty on the Tramp's face turns to joy as the film fades to black.