2040-2045: In the years after the cataclysmic Yellowstone eruption there is massive economic dislocation as populations flee Datum Earth to myriad Long Earth worlds. Sally, Joshua, and Lobsang are all involved in this perilous work when, out of the blue, Sally is contacted by her long-vanished father and inventor of the original Stepper device, Willis Linsay. He tells her he is planning a fantastic voyage across the Long Mars and wants her to accompany him. But Sally soon learns that Willis has an ulterior motive for his request: he needs her help to trace an advanced alien technology which, he believes, will help mankind’s post-Yellowstone recovery.

Meanwhile U. S. Navy Commander Maggie Kauffman (introduced in The Long War) has embarked on an incredible journey of her own, leading an expedition to the outer limits of the far Long Earth.

For Joshua, the crisis he faces is much closer to home. He becomes embroiled in the plight of the Next: the