“Their trademark world building and questions of morality remain intact . . . The explosive cliffhanger ending—also now something of a trademark—promises one final return to the series.” — Booklist

The fourth novel in Terry Pratchett and Stephen Baxter’s bestselling series, which io9 calls “a brilliant science fiction collaboration.”

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.

The complete list of books in the Long Earth series include:

• The Long Earth
• The Long War
• The Long Mars
• The Long Utopia
• The Long Cosmos

It is the middle of the 21st century

After the cataclysmic upheavals of Step Day and the Yellowstone eruption, humanity is spreading further into the Long Earth. Society, on a battered Datum Earth and beyond, continues to evolve.

And new challenges emerge.

Now an elderly and cantankerous AI, Lobsang is living with Agnes in an exotic, far-distant world. He’s determined to lead a normal life in New Springfield—they even adopt a child. But there are rumors, strange sightings in the sky.

On this world, something isn’t right . . .

Millions of steps away—learning about a hidden family history and the father he never knew—Joshua receives an urgent summons from New Springfield.

Lobsang has come to understand that what has blighted his Earth is a threat to all the worlds of the Long Earth. To counter this threat will require the combined efforts of humankind, machine, and the superintelligent Next.

And some must make the ultimate sacrifice . . . "[T]he co-authors have created a tighter, more focused narrative that moves faster than its predecessors. The explosive cliff-hanger ending-also now something of a trademark-promises one final return to the series.