"The Last Leaf" opens with a description of the winding streets of Greenwich Village, New York City, where artists flock to find low-cost apartments with north-facing windows and Dutch-style gables. After they meet at a restaurant, Sue and Johnsy, the story's protagonists, discover they have similar tastes in art, food, and fashion.
In May they get a studio apartment together in Greenwich Village. By November, a pneumonia pandemic has hit New York. Johnsy, being used to California's warmer weather, falls ill. A doctor assesses her, and informs Sue that Johnsy’s chances of survival are one in ten, largely because she has lost the will to live.
In Johnsy's room, Sue works on an illustration for a magazine. She hears Johnsy quietly counting the leaves left on the old and struggling ivy vine that clings to the brick of the neighboring building. Johnsy says there are only six left, and she has known now for three days that she will die when the last leaf falls.
Sue asks her not to speak such nonsense and commands her to go to sleep. Sue goes downstairs to ask old Behrman to pose for her drawing. Sixty-year-old Behrman is a painter, but he has never found success. He always speaks of creating a masterpiece, but he never starts it. He drinks heavily and feels he has a special responsibility to protect the young women who live upstairs. Sue tells him about Johnsy's superstitious belief that her life is connected to ivy leaves. Behrman laments and denounces such foolishness.
Johnsy is asleep, so Sue lowers the window shade. In the other room, she and Behrman look unhappily at the rain and snow and wind threatening the final ivy leaves. Behrman poses and Sue draws him.
In the morning, Johnsy asks Sue to raise the shade. Miraculously, a single leaf remains attached to the vine, having withstood the night's storms. Johnsy says it will surely fall by night, and then she too will die. But the leaf doesn't fall. In the morning, Sue raises the shade to reveal that the leaf is still attached. Johnsy stares at the leaf for some time. She then asks Sue for some broth; she now believes the leaf is there to remind her that it is sin to wish to die.
The doctor visits and says Johnsy's chance are now fifty-fifty. He tells Sue he must now visit Behrman, who has a critical case of pneumonia and needs to be taken to hospital.
The next day the doctor says that Johnsy is beyond any danger. Behrman, however, passed away after having been ill for only two days.
That afternoon, Sue goes to Johnsy and puts an arm around her. Sue explains that Behrman died; two days earlier the building janitor found Behrman in his room helpless with pain. He was soaked through with rain, and the janitor wondered why he would have been out in the miserable night. He then found a lantern still lit, a ladder, and a palette with green and yellow paints on it.
Sue asks Johnsy if she ever wondered why the last leaf never moved with the wind. It's because Behrman painted it the night the actual last leaf fell, and he contracted pneumonia in the process. It was Behrman’s greatest masterpiece, Sue says.
