Garden of Forking Paths

 An Asian spy for Germany named Yu Tsun, while trying to pass on some information to his commanding officer through a murder he would commit, meets with Stephen Albert and discusses the labyrinth created by Ts'ui Pen. The labyrinth, as proposed by Albert, Is the novel that Pen wrote with the intention that, "all men would loose themselves inside it."

Before speaking to Albert, Tsun imagines this labyrinth as somewhere remote, such as on the top of a mountain, hidden drowned under rice paddies, or even beneath the sea. The intersections and paths being made from pavilions, twisting paths, and rivers; an ever growing maze that somehow would take place in both the past and in the future. While pondering this he forgets that he is being chased by captain Madden, someone who Tsun believes is after him because Madden thinks he is a spy. On meeting Tsun, Albert belives that Tsun is Hsi P'eng, a consul from China, and allows him to come in after Tsun mentions that he is the descendant of Ts'ui Pen. Tsun decides to talk about Pen's garden after thinking that Madden could not get there within an hour.

Tsun believes that the book is nonsense, but Albert refutes this by proposing that the book itself is the labyrinth, explaining that Pen's statements that he was retiring to write a book and retiring to build a labyrinth were stated at different times, and thus recognized as separate activities; despite this the two activities were actually one and the same. He proposes how a book could be infinite, with the first and last pages being the same, and compares it to Scheherazade's tale of The Thousand and One Nights.

The phrase "I leave to various future times, but not to all, my garden of forking paths" was part of Pen's dedication in the book. This is what led Albert to believe that the conflicting chapters of the novel. He then describes a universe where all possible choices happen, and that sometimes the choices converge. (This is a part of an interpretation of the world where if something could happen; it would, did, and will.) Albert notes that time is omitted, and uses this to elaborate on the aforementioned concepts. 

Despite Tsun insisting that he is grateful for this discussion in all timelines, Albert insists that no matter what there is a timeline where they were enemies, even mentioning that he believes P'eng (Tsun) but that there is a timeline where all of this has happened but he is in error. Tsun kills Albert, believing that the name of the target city has gotten back to Berlin, and accepts that he is to be executed.

There are several interpretations of certain characters, as Madden himself never speaks and therefore we do not know if he actually suspects that Tsun is a spy before Tsun flees. (However, there is stated to be two more pages which are missing from the short story.)

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TLDR: The book is the Maze, the text discusses the theory of each decision or event creating a set of branching timelines, and any of those timelines might converge due to some specific events just being different routes to a similar result.

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As an aside to this whole thing; the idea that anything that can happen, will happen in some alternate timeline is a concept that some find uncomfortable as it seems to strip away free will. This can be argued either way, but is better left to philosophers. I would expand a bit more but it is late and I am tired. (Short version is: You have free will because no matter what happens in other timelines, you only really experience one and make an individual choice based on that experience, leaving the total of that experience as you. "You" from another timeline that made any number of different choices is not actually you, and might not be treated as such. This whole thing is an interesting thought experiment but again, tired and will probably just keep repeating myself if I keep writing.)