The Post Office at the Edge of the Kuiper Belt may or may not exist. In fact it probably doesn't. But this improbability doesn't mean that it actually doesn't exist at all....or for that matter, that it probably doesn't exist anywhere as remote and inhospitable as the Kuiper Belt. Which is or could be a pity; that depends.
This book presumes it does exist or will come into existence at some time over the next 25 years - the time it will take for the Navis-Spei spaceship to get there with its all-important letter addressed as follows: To Whom It May Concern, and with at least one intelligent creature, either biological or Android, or a combination of both, to post it!
The Navis-Spei set off from Woomera in the South Australian Outback on the eve of the 1st of November 2027, moments before planet Earth was overwhelmed by a chain reaction of nuclear catastrophes; it was carrying 50 carefully chosen people whose job it was to continue the evolutionary tradition of ensuring survival of their species.
Conceived some time in 2027 by the United Nations General Assembly, in anticipation of the inexorable and definitive extinction event for humanity, and mindful of the 1945 Charter which established the UN, the MUST project was stood up as the final throw of the survival dice for the human genome. A colony of 50 people was given the job of posting a letter with the hope that at some future time, an intelligent extra-terrestrial traveler would happen to read and perhaps understand something about the human species and its origin...and perhaps even understand what went wrong with it that it should self-destruct after less than 50,000 generations.
Their challenge was enormous: the compilation of a condensed history of the human species from its origin through to its moment of annihilation in 2027.

This book was suggested by the seemingly irrational behavior of the Russian President, Vladimir Vladimirovich Putin in February 2022, when he decided to conduct a "special military exercise" in Ukraine, which the rest of the planet read as "invading" Ukraine, on the pretext that it was still part of mother Russia, whether it liked it or not, and not a Sovereign Country, which it claimed to be. Ukrainians argued that with its own democratically elected government it was independent of Russia, and it expressed a desire to join the European Union, which the EU supported in principle.
And so a dreadful and unnecessary war resulted and raged for several years, destroying everything in its wake, on both sides. The Russians were offered peace but they didn't know what to do with it! When tactical, low-yield nuclear weapons were eventually used by the Russians as a last resort to snatch victory from the jaws of defeat, their military assets and reputation as a world power were annihilated by the promised US-led response. Not only was this an ignominious extinction event for Russia, but the ripple effects precipitated the 6th and final extinction event for planet Earth.
Mixed up in this mess was a fundamental misunderstanding of Christianity and a senseless feud between Unitarians and Trinitarians which reached back in history to the year 325CE and the Council of Nicaea.

To succeed in its Mission, 50 people have to put aside their differences on Earth, reinvent themselves as humans and work together to survive on a space ship called the Navis-Spei.... even if it was just for the first 25 years of their journey. After that, survival of the species over the subsequent 5,975 years it would take to reach a more hospitable solar system would be a miracle.