In the middle of the twenty-first century. The cataclysms of Step Day and the Yellowstone eruption have sent humanity out into the Long Earth. Society, on a battered Datum Earth and beyond, continues to evolve. And new challenges emerge. In a far-distant world, a cantankerous and elderly Lobsang lives with Agnes in the community of New Springfield and endeavours to lead a normal life. They even adopt a child. But there are rumours of hauntings, strange sightings in the sky. On this world, something isn't right. Millions of steps away, Joshua receives an urgent summons from New Springfield. Lobsang believes that what is blighting his Earth now threatens all the worlds of the Long Earth. To counter this will require the combined efforts of humankind, machine and the super-intelligent Next. And some must make the ultimate sacrifice...