The fourth novel in Terry Pratchett and Stephen Baxter's internationally best-selling Long Earth series, hailed as "a brilliant science fiction collaboration...a love letter to all Pratchett fans, readers, and lovers of wonder everywhere" (Io9).

It's 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 50s, searches for his father and discovers a heretofore unknown family history. And the superintelligent posthumans 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.