A new America called Valhalla grows restless under the controlling long arm of the Datum government, while all of the Long Earth is infused by the song of the trolls who are starting to react to humanity's thoughtless exploitation, bringing humankind to the brink of war.

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...