2040. The Long Earth is in chaos. . . .

The cataclysmic Yellowstone eruption is shutting down civilization. Whole populations flee to the relative safety of myriad stepwise Earths. Sally Linsay, Joshua Valiente, and Lobsang have all been involved in the perilous post-eruption clean-up.

But Joshua faces a crisis close to home. From a long childhood hidden deep in the Long Earth, a new breed of young, super-bright post-humans is emerging'but 'normal' human society is turning against them, driven by ignorance and fear. For Joshua, caught up in the conflict, a dramatic showdown seems inevitable.

Meanwhile, US Navy  Commander Maggie Kauffman embarks on an incredible journey, leading an expedition to the unexplored limits of the far Long Earth.

And Sally is contacted by her long-vanished father, Willis Linsay'inventor of the original Stepper device. Ever the maverick, he is planning a fantastic voyage of his own'across the Long Mars. But what is his true motivation?

For Joshua, for humankind, for the Long Earth itself'everything is different now.