The Long Utopia (Long Earth Series #4)

The dazzling new science fiction adventure from the extraordinary imaginations of Terry Pratchett and Stephen Baxter — the fourth novel in a collaborative series that has been hailed as 'sense-of-wonder SF at its best' (Independent on Sunday).

2045-2059. After the cataclysmic upheavals of Step Day and the Yellowstone eruption humanity is spreading further into the Long Earth, and society, on a battered Datum Earth and beyond, continues to evolve.

Now an elderly and cantankerous AI, Lobsang lives in disguise with Agnes in an exotic, far-distant world. He's convinced they're leading a normal life in New Springfield — they even adopt a child — but it seems they have been guided there for a reason. As rumours of strange sightings and hauntings proliferate, it becomes clear that something is very awry with this particular world.

Millions of steps away, Joshua is on a personal journey of discovery: learning about the father he never knew and a secret family history. But then he receives a summons from New Springfield. Lobsang now understands the enormity of what's taking place beneath the surface of his earth — a threat to all the worlds of the Long Earth. To counter this threat will require the combined efforts of humankind, machine and the super-intelligent Next.
And some must make the ultimate sacrifice.