2040-2045. In the years after the cataclysmic Yellowstone eruption, populations flee Datum Earth to myriad Long Earth worlds. Sally, Joshua and Lobsang are all involved in this perilous work when Sally is contacted by her long-vanished father. He tells her he is planning a fantastic voyage across the Long Mars and wants her to accompany him. For Joshua, the crisis he faces is much closer to home. He becomes embroiled in the plight of the Next: the super-bright post-humans who are beginning to emerge from their "long childhood" deep in the Long Earth. Ignorance and fear are causing "normal" human society to turn against them - and a dramatic showdown seems inevitable... .