Stephen Baxter-Terry Pratchett

“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…