Carefully reallocating the Time of Discworld to where it is most needed, Monk of History Lu Tze and his apprentice begin a literal race against time when the world's first truly accurate clock threatens to stop Time forever.

The Next--the hyper-intelligent post-humans--realize that the missive they received from the center of the galaxy contains instructions for kick-starting the development of an immense artificial intelligence knows as The Machine. But to build this computer the size of an Earth continent, they must obtain help from the more populous and still industrious worlds of mankind.

Lobsang's pursuit of a human life, Joshua's search for his father and the adaptation efforts of "the Next" post-humans are challenged by a voracious alien race that would conquer and colonize the Long Earth. "2045-2059. Human society continues to evolve on Datum Earth, its battered and weary origin planet, as the spread of humanity progresses throughout the many Earths beyond. Lobsang, now an elderly and complex AI, suffers a breakdown, and disguised...