A two-dimensional inhabitant of Flatland encounters a three-dimensional sphere, triggering a radical shift in his perception of reality. The protagonist, A. Square, navigates a rigid, hierarchical society where social status is determined by the number of sides one possesses. His objective is to reconcile his newfound knowledge of higher dimensions with the dogmatic, flat-minded laws of his world. He faces opposition from the ruling class, who view his claims of a third dimension as dangerous heresy, forcing him to confront the logical constraints of his existence through a first-person narrative framework.

Readers frequently highlight the cleverness of the book's premise, noting how it effectively uses geometry to critique social stratification. Discussion often centers on the accessibility of the mathematical concepts, which remain clear despite the author's Victorian prose style. Critics often point to the work as a foundational text for speculative fiction that prioritizes intellectual inquiry over traditional character-driven drama. The atmosphere is described as clinical yet imaginative, providing a distinct experience that challenges the reader to visualize dimensions beyond their own. Many appreciate the balance between the dry, analytical tone and the underlying satirical bite directed at the rigid norms of the nineteenth century.