One of the examples given in Flatterland concerns how to escape from a black hole. For an explanation of this diagram, see the file page.
Almost 100 years after A. (which we find out stands for Albert) Square's adventures that were related in Flatland, his great-great-granddaughter, Victoria Line (Vikki), finds a copy of his book in her basement. This prompts her to invite a sphere from Spaceland to visit her, but instead she is visited by the "Space Hopper" (a character looking somewhat like the "Space Hopper" children's toy with a gigantic grin, horns and a spherical body). The Space Hopper, more than being able to move between Flatland and Spaceland, can travel to any space in the Mathiverse, a set of all imaginable worlds. After showing Vikki higher dimensions, he begins showing her more modern theories, such as fractional dimensions and dimensions with isolated points. Topology and hyperbolic geometry are also discussed, as well as the Projective "Plain" (complete with intersecting "lions") and the quantum level. Hopper and Victoria also visit the Domain of the Hawk King to discuss time travel and the Theory of Relativity.
Vikki, while traveling in the Topological Dimension, also meets a one-sided cow named Moobius (derived from the Möbius strip) who sells her milk in Klein bottles (the strip and the bottle both being one-sided topological figures).
The Doughmouse, the Harsh Mare and the Mud Hutter are the counterparts in Topologica (the rubber-sheet continent) of Carroll's Dormouse, March Hare, and Mad Hatter, respectively. The Doughmouse works with a dough tea set, dough being flexible.