"Leaf by Niggle" is the story of a small, humble artist named Niggle, living alone in a world that does not really value his work. Despite this social ostracism, Niggle has an inner desire to create something beautiful, so he perseveres in his artwork. All of his time is consumed by working on his magnum opus, a giant, detailed landscape centered around a large tree. The masterpiece originally began as a small leaf, but as if of its own accord, the piece of art kept growing and filling out until it seemed to become a world unto itself.
While Niggle is slaving away over this tree, his neighbor, Parish, routinely asks him for help with various things, including his wife's sickness, which continually interrupts Niggle's work and thought process. But Niggle does these acts of service anyway. He eventually comes down with a cold as a result of cycling out to Parish's house in the rain.
One day, men appear at Niggle's door, telling him that it is time to go on his journey. Niggle realizes that he has not prepared for the journey, but he is whisked away anyway. As a result of his unpreparedness, he finds himself at "the Workhouse," a sort of white, sterile hospital, where he must perform various menial tasks and duties every day. This routine continues for a while before Niggle finds himself the subject of conversation between two Voices, who discuss his situation before agreeing to send him to "the next stage."
This "next stage" takes the form of a beautiful, undeveloped plot of land at the end of the railway line, where the Porter leaves him. There he finds his Tree, the piece of art he had been laboring on in life, full and complete and fully realized in physical, three-dimensional space. Ecstatic, Niggle begins to mold the rest of the landscape, working day after day to create something beautiful from the natural raw material of the land. His neighbor, Parish, eventually joins him, and the two collaborate to create a beautiful landscape. After a while, Niggle walks to the far borders of the land, where he discovers that its name is "Niggle's Country"; he then follows the guide to the realm of the Mountains.
Back in Niggle's hometown, the councilmen discuss his departure, noting that he did not seem to be of much use to society. The Voices, by contrast, speak highly of the land Niggle shaped before his journey into the mountains, joyfully recounting the new name some have called the lands: Niggle's Parish.
