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 as a human attempts to live a 'normal' life on one of the millions of Long Earth worlds. His old friend, Joshua, now in his fifties, searches for his father and discovers a heretofore unknown family history. And the super-intelligent post-humans known as 'the Next' continue to adapt to life among 'lesser' humans. But an alarming new challenge looms. An alien planet has somehow become 'entangled' with one of the Long Earth worlds and, as Lobsang and Joshua learn, its voracious denizens intend to capture, conquer, and colonize the new universe--the Long Earth--they have inadvertently discovered. World-building, the intersection of universes, the coexistence of diverse species, and the cosmic meaning of the Long Earth itself are among the mind-expanding themes explored in this exciting new installment of Terry Pratchett and Stephen Baxter's extraordinary Long Earth series"-- provided by publisher.