The story describes a
two-dimensional world inhabited by
geometric figures (flatlanders); women are
line segments, while men are
polygons with various numbers of sides. The narrator is a
square, a member of the
caste of gentlemen and professionals, who guides the readers through some of the implications of life in two dimensions. The first half of the story goes through the practicalities of existing in a two-dimensional universe, as well as a history leading up to the year 1999 on the eve of the 3rd Millennium. On New Year's Eve, the Square dreams of a visit to a
one-dimensional world, "Lineland", inhabited by men, who are lines, while the women are "lustrous points". These
points and lines are unable to see the Square as anything other than a set of points on a line. Thus, the Square attempts to convince the realm's
monarch of a second dimension but cannot do so. In the end, the monarch of Lineland tries to kill the Square rather than tolerate him any further. Following this vision, the Square is visited by a
sphere. Similar to the "points" in Lineland, he is unable to see the three-dimensional object as anything other than a
circle (more precisely, a
disk). The Sphere then levitates up and down through Flatland, allowing the Square to see the circle expand and contract between a
great circle and small circles. The Sphere then tries further to convince the Square of the
third dimension by dimensional analogies (a point becomes a line, a line becomes a square). The Square is still unable to comprehend the third dimension, so the Sphere resorts to deeds: he gives information about the "insides" of the house, moves a tablet through the third dimension, and even goes inside the Square for a moment. Still unable to comprehend the third dimension, the Square is taken by the Sphere to the third dimension, Spaceland. This Sphere visits Flatland at the turn of each millennium to introduce a new
apostle to the idea of a third dimension in the hope of eventually educating the population of Flatland. From the safety of Spaceland, they can oversee the leaders of Flatland, acknowledging the Sphere's existence and prescribing the silencing. After this
proclamation is made, many witnesses are massacred or imprisoned (according to caste), including the Square's brother. After the Square's mind is opened to new dimensions, he tries to convince the Sphere of the theoretical possibility of the existence of a
fourth dimension and higher spatial dimensions. The Sphere at first scoffs at the idea of higher dimensions, just as the Square had done, showing that his comprehension is not as broad as he had thought. Still, the Sphere returns his student to Flatland in disgrace. The Square then has a dream in which the Sphere revisits him, this time to introduce him to a
zero-dimensional space, Pointland, of whom the Point (sole inhabitant, monarch, and universe in one) perceives any communication as a thought originating in his own mind (cf.
Solipsism): {{quote|"You see," said my Teacher, "how little your words have done. So far as the Monarch understands them at all, he accepts them as his ownfor he cannot conceive of any other except himselfand plumes himself upon the variety of
Its Thought as an instance of creative Power. Let us leave this god of Pointland to the ignorant fruition of his omnipresence and omniscience: nothing that you or I can do can rescue him from his self-satisfaction." The Square recognises the identity of the ignorance of the monarchs of Pointland and Lineland with his own (and the Sphere's) previous ignorance of the existence of higher dimensions. Once returned to Flatland, the Square cannot convince anyone of Spaceland's existence, especially after official
decrees are announced that anyone preaching the existence of three dimensions will be imprisoned (or executed, depending on caste). For example, he tries to convince his relative of the third dimension but cannot move a square "upward," as opposed to forward or sideways. Eventually, the Square himself is imprisoned for just this reason, with only occasional contact with his brother, who is imprisoned in the same facility. He cannot convince his brother, even after all they have both seen. Seven years after being imprisoned, "A. Square" writes out the book
Flatland as a
memoir, hoping to keep it as posterity for a future generation that can see beyond their two-dimensional existence. ==Social elements==