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...

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 rescue 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...